Oct 28th 2019: Updating for 6.0. Q0-77 and Personal Warbot seem to be fixed. Command stims back. Presence amps are out. Shae Vizla still rocks at over 10k dps. Z0-0M on the cartel!

Dec 23rd 2018: Updated for 5.10, Paxton Rall and recent tank findings.

Apr 21st 2018: Updated for 5.8.

Feb 27th 2018: Added D-R3D parse.

Nov 29 2017: Added Darth Hexid notes

Nov 21sr 2017: Updated for patch 5.5.1a. Added some new parse numbers. Most companions now do 200-300 more dps. Tested the melee droid, he's a fair Scorpio replacement.

March 19th 2017: Updated for patch 5.1.3 and the fact that Shae Vizla is OP AF.

March 5th 2017: Updated for patch 5.1.2 and adjusted recommendations.

Febuary 9th 2017: Updated for patch 5.1.1. Added extensive heal parses.

Febuary 3rd 2017: Updated for patch 5.1

September 4th 2016: Added Eternal Championship tips section.

August 24th 2016: Added Level Sync Info and some HM Star Fortress parses.

August 16th 2016: Added more tips on Solo HM FPs.

August 8th 2016: Updated known bugs list. Poor Veeroa Denz. Other minor clean up.

August 6th 2016: Added Most Effective Companions section.

August 2nd 2016: Added Heroics, Star Fortress and Solo Flashpoint Tips.

August 1st 2016: Cleaned up formatting a bit. I've also been adding some parses and notes as I find them.

July 26th 2016: Updated for patch 4.6a and all the changes since 4.0.

June 26th 2015: Added Links to Suggestion Posts for fixing companion DPS and Legacy ability imbalances

June 14th 2015: Updated companion parse data and rechecked Legacy abilities. Added Healer Parses! Removed Old HK part info. Added notes on Nico Okarr.

June 9th 2015: Added Devoted Allies companion gear info. Expanded Presence section. Added note on player debuffs.

Oct 9th 2014: Added Companion Battle section and alacrity note.

July 20th 2014: Swapped Tank aug priority. Shield > Absorb.

July 19th 2014: Added DPS Parse summary.

July 13th 2014: Added Parse Examples/results, check out Vector!

July 12th 2014: Minor corrections. Added parse info on all Heroic Moment Skills!

Jan 12th 2014: Updated Gearing section with differences, augs and improved recommendations. Couple more notes on HK and Treek.

Dec 29th 2013: Updated Parse section with Parsec data. Added HK Droid part Mat list.

Influence:
As you finish crew skill missions, complete some story missions, or give gifts, your influence with a companion increases. Starting at level 1 and capping out at level 50.

Dulfy has an excellent guide on increasing your influence.

In addition, some companions will get Influence bonuses from PVP or Star Fortress.

For each influence level, you get +50 presence with that companion. This makes it the most important factor in combat effectiveness.

Presence:
Presence affects your companions Health, Heals and Damage. Health being the largest improvement you'll see.

You’ll get +100 legacy presence from unlocking the human species. If you have not yet, you can find it under legacy and just purchase there.

Finish all your companion quest conversations. This means get their influence to 8000-10000 and talk till they are worn out. You’ll get a +10 permanent (legacy) presence bonus for each companion. This can add up to 200 on imp and 200 on pub side.

Datacrons also give presence. They are now legacy as well, so they are worth the work once.

Drinks from cantinas give a stack-able presence bonus which are great to use for any occasion.

Command stims are also available and are not a bad choice for heroics (once again craftable in 6.0).

You can now roll presence on gear (amps) since 6.0. Sometimes you can get some high bonuses like +50.

The legacy bound relics from the rakghoul events give a very nice presence bonus and I'd highly recommend them for leveling.

Class Buffs:
Your companions benefit from class buffs, just like you do. Make sure they have them on before battle. Finish your chapter 2 with all 4 classes and you’ll have the legacy class buffs for all your characters.

Debuffs
Each class has attacks that leave targets more vulnerable to certain attacks. For instance, if you play a sniper you and your companion may do 5% more ranged damage. If you play a warrior, you both may do 5% more melee damage. There is a great article on it here.

Unity:
This skill reduces the damage you and your companion take. You can purchase it, or get a lightside character to unlock it for your legacy. This skill is easily forgotten but can save your hide in a tough fight.

Sacrifice:
Can be used before mounting up to get a free heal. It's not really useful.

Heroic Moment:
This skill heals you and your companion for the duration as well as enabling any of the cool heroic moves you have unlocked (Chapter 3 with any of the 8 classes). Since these are heavy hitting abilities, plan them out as well as possible. You may want to use a stun before your channeled abilities like flame thrower or orbital strike.

Level Sync and Your Personal Combat Effectiveness:
When you go to a lower level planet for things like heroics, your combat effectiveness and effective level is reduced. They do this by "capping" your health, force/tech power and armor at the max possible for the planet level.

This means that if you're farming heroics, much of your higher level gear is only useful for secondary stats, like alacrity, critical or defense.

For example on tatooine I can take off all of my gear except for my main and offhand and I'm still at Tech Power cap. On Ilum I can take off 3-4 pieces of gear with no effect.

Since power or mastery relics are useless for heroics, you may consider absorb shield, mending (triggered by any self heal) or critical relics since these are not capped or reduced. Depending on your spec these relics might cover all your health issues and let you run with a dps comp.

Level Sync and Your Companion:
If you solo/duo heroics with a companion often, you may want to consider some of the above tips, to get your presence up like rakghoul relics, command stim and a corellian cocktail. Presence is not capped, so although you and your companion are level 18, your 4400 presence is in full effect and is really the only way to increase your overall damage output on lower planets. Usually my companion has 2-3x as much health and up to 3x more damage than I do. This means a duo group with a good DPS companion could double the dps output of 4 real level 70 average players.

DPS:
Shae Vizla is the highest DPS companion in the game right now, parsing 10.5k on a dummy, due to a major bonus to her AOE skill.

Any companion with 2 weapons (blasters or sabers) will be excellent for DPS, parsing around 8000.

Q0-77, Nico, Vette, Hamdil Tre, Theron Shan, Andronikos Revel and Ensign Temple all use 2 blaster pistols and are top Ranged DPS after Shae. I recommend one of them for most fights.

Ashara Zavros, Veeroa Denz and Master Ranos are the highest melee DPS companions.

D-R3D does not channel his AOE attack (bug) so his dps is slightly less than other 2 weapon dps.
Heals:
If you are in fights that don't have a very high healing requirement, I'd recommend using any of the high DPS companions above (with 2 weapons, not Shae Vizla) and disabling their Channeled heal.

Z0-0M is the highest heals (because of hidden bonus AOE) (tests coming soon).
Second is Paxton Rall, he has a great Life Jolt ability that does an AOE heal (instead of bubble) and a root.
After that, any ranged companion and then any melee healer.

Melee companions can heal just fine, they just may have a small delay in their heals while they move to new targets.

Tank:
For short fights, trash or very mobile bosses, any high DPS Melee companion, they will stay in melee range and deliver a high amount of threat from their damage.

For long fights, or bosses that won't rush your companion, consider using a high dps ranged companion, Taunts are more effective at range and over a long fight (500k) you could get 5 mil threat on a melee and 15 mil threat on a ranged.

I'm taking Dr Lokin off my list for tanks.. He's great because he had no cooldown on his jumps, but he doesn't have real taunts in my tests, so over a long fight he wont be near other comps.

Best Leveling Companion:
1. Shae Vizla for dps, Q0-77, Nico Okarr or Paxton Rall for heals, Master Ranos for tank
2. Darth Hexid, K1-Z3N, T4-1D or TY-4N are standard blaster users with minimal bugs (bought or unlocked for collections)

Cartel Companions:
Most Cartel companions are bugged in some way (need testing since 6.0, some were fixed). K1-Z3N has no known bugs (but didnt get 5.5 damage boost like others). T4-1D or TY-4N functions like a normal blaster riffle user for DPS and Heals.

Damage Skills and Tips:
I often turn off the stun so I can use it manually on harder bosses. In my testing, there is a damage bonus for companions with 2 weapons (blasters or light sabers).

Healer Skills and Tips:
If you don't need a ton of heals, you can get more dps by disabling the channeled heal. Also, comps are not good at prioritizing heals so, try to keep the damage on 1 player at a time.

Tank Skills and Tips:
Tank companions are great now. They have multiple absorb and damage reduction skills, even an AOE Pull, which lets you gather up groups for AOEs.

PVP:
Remember when you stun a companion, the resolve is shared with the player, so you might want to turn off CCs on your comp. Keep your heroic moment and unity handy, it can make a big difference.

Companion Battles:
This is a great use for your guild flagship or guild headquarters. Meet up, duel and tell your companions to fight it out.

Remember to bring your presence buffs (cantina drink, command stim) and if you're really crazy you can craft a full set of command gear and aug for presence The rakgul vendor has some great presence relics as well.

Decide if unity, heroic moment or skill micromanagement is legal before you start. Using a stun or kill shot at the right moment can sometimes make a big difference.

Keybindings and Interface:
You can rebind any of your companion skills. Control + whatever can be a pain. Especially for healers, you’ll want to make sure your companion is attacking anything that is trying to hurt you.

As heals, if you use operations frames instead of Group frames, you can set your group member’s companion as Focus Target (Alt F) so it’s easy to keep track of it’s health during a fight.

Heroics Tips:
Many people Solo or Duo Heroics using companions. Its one of the places they really shine late game.

First off, having planet level appropriate gear matters for heroics. This is why I don't recommend them for solo leveling, solo FPs are much better in that regard.

If you have 2 people, make sure only 1 of you has your companion set to heal. 1 Companion can heal a full group easy.

If your companion is set to heal, be sure to turn off the channeled heal for most fights. I find I only need to turn it back on if I pull a whole room on Belsavis or something.

If you are well geared and feel comfortable with your survival, consider going DPS with a DPS companion, as this is the fastest way to complete these. You'll have to judge your own comfort level though.

Consider using Shae or a companion with 2 weapons. Veeroa Denz, Master Ranos, Ashara, Vette, Theron, Hamdil Tre..

Level up your companion. Once you've decided which one you want to use for these, level them up as high as you can. The higher you get them, the easier/better life will be. You might even want to toss on a couple thorn relics, a command stim and a drink from the cantina to increase your presence if you really let your companion do most of the work.

Dulfy Heroic Guide - Imp

Dulfy Heroic Guide - Pub

Heroic Guide and Times per by ArthurDDL

Similar spreadsheet with republic side by Jessabeans

Star Fortress Tips:
Star Fortress is probably my favorite content. I love companions, soloing flashpoints, free companion influence and free decos.

Dulfy's Star Fortress Guide

Black Bantha's Star Fortress Guide

All the Heroic tips above still apply for star fortress. Some even more so because there is no planet level adjustment in there.

In story mode, the flashpoint should be pretty easy. I can complete them in about 15 minutes. 3 Decos (80k-1.2m each), 100k, and 750 companion influence is sure not bad for the time it takes to complete 1 PVP match.

For heroic mode, I hardly see deco drops.. Although I've heard rumor the paladins drop bracers, I've never seen it. I have gotten the speeder off the final boss twice so far.

If you have your influence with one of the alliance specialist to 4 you can use the heroic buffs, which make a giant difference. If you are at 10 with all the specialist you can pick up special reusable skills in the mission (2 in the first half, 2 in the second), they are awesome, feel free to use them often, maybe saving the turret for a boss fight. If you don't have the influence yourself yet, you may want to get a friend to join you on the heroic version, the fights go very fast that way.

Be sure to get Veeroa Denz from Narshada as she is a super star DPS. Hamdil Tre is a great double blaster user if you can't stand all the fuss around Vette or Theron.

Eternal Championship Tips:
Doing your weeklies for championship can pay off well. Mostly in isos. The legacy weapons are pretty awesome also as they show your color crystal on the sides.

The championship is mostly about mechanics, but you'll also want a good gear level and to know your rotation as the faster the bosses die, the safer you'll be.

I would NOT recommend doing this in heal spec, even with a good dps or tank companion it's just painful..

Most people go DPS with their companion in heal stance. I prefer to go DPS/DPS on the first few bosses, then swap my companion to heals as things get harder. You'll definitely want to do that if you're going for a speed run achievement.

If you're companion is set to heals, It's a good idea to practice turning the channeled heal on and off during the fight depending on the damage you're taking. There are many phases when your companion can help out by DPSing an ad or something else.

Although the default advice is always use a ranged companion for healing when you have mechanics... I have not seen any advantage to that in the championship. The Breaktown Brawler fight has a reflect that will hurt any ranged companion. Ironically I've only had to put a ranged companion on follow, and never had a problem with a melee in there.

Other than that, learn the mechanics, usually that means killing, interrupting or stunning ads and staying out of most things on the floor.

Dulfy has an excellent guide here

Solo Flash Point Tips
Solo Flash Points are in my opinion the fastest way to level. They are great for conquest now also and quick kills.

You can get the 30% xp bonus for your character. You can get 25% flash point XP consumables for cheap. Gear doesn't matter, empty shells work just fine. Most importantly, you get your companion AND a "Jesus Droid" so the deck is stacked in your favor..

Set your companion to DPS. The Jesus droid has you covered.

Hit everything in the FP at least once. Otherwise your companion may never attack and the Jesus droid will sit there tanking the mob forever.

Go DPS if you're comfortable with it, more damage is always better.

Take a friend. You both get a companion and a Jesus droid, so you can roll through the FP with a small army. Double Heroic Moments can just decimate a boss in 7 seconds as well Swap lead if someone gets the message saying they can't summon droid.

List of Flashpoints and Solo Modes with Levels

Master Flashpoints Solo/Duo
I can't advise doing these solo unless you're stealth, it's just a ton of work getting through ads. Stealth is even better now though and make some flash points as lucrative as pvp for cxp.

Gear matters, as many of the enrage timers are tight, or damage increases over time. The same for companion level, 50 is preferred.

Also keep in mind some of the phases deal much less damage than others, if you turn off the channeled heal from your companion on those, you'll get a nice dps bonus. Just that alone helped me get through red reaper, as my companion could help kill the rooting ads.

Look for talents that can help with a particular boss. Damage reduction ones are usually important. The break stun and jump to target ones can be crucial for melees to keep the fight moving. Reflect is very nice on some bosses.

Unity can help a lot, and if the fight is long enough, heroic moment will pop a second time, so be sure to start the first one early.

DPS/DPS is also a crazy option on some fights, if you can share agro and time your cooldowns right, it might help you make it through some of the harder enrage timers. If ads are dead, they are not causing you damage anymore In a fight Veeroa Denz does maybe 3k dps tops in heal spec with channeled disabled, she can do almost 8000 dps in dps stance, and the armor debuff might help all of your damage if you lack one in your tree.

When I duo flashpoints, sometimes it pays to have 1 tank comp and 1 heal comp as healing companions get confused when they have to balance healing 4 people at once.

If you are a stealth duo and your companion dies, you can quickly re-summon it in a fight by stealthing, then using rocket boots before re-entering combat.

Parsing:
Although the raiding part of parsec was disabled, the app is still great for seeing companion DPS and the only one I know of that even shows companions now. It takes some tech skills to get it working though.

DPS Parse on Rishi debuffed Operation dummy 1.5m:
Level 1, Shae Vizla (Ranged, 1 Pistol) 4914 - 5.10
Level 1, Nico Okarr (Ranged, 2 Pistols) 4013 - 5.10
Level 1, Paxton Rall (Ranged, 1 Pistol) 3938 - 5.10

Tank spec DPS Parse on Rishi debuffed Operation dummy 0.5m:
Level 1, Nico Okarr (Ranged, 2 Pistols) 1648 dps /48,582 threat - 5.10
Level 1, Paxton Rall (Ranged, 1 Pistol) 1746 dps /45,839 threat - 5.10
Level 1, Master Ranos (Melee, 2 Saber) 1839 dps /17,986 threat - 5.10

Heal spec DPS Parse on Rishi debuffed Operation dummy 0.5m:
Level 1, Shae Vizla (Ranged, 1 Pistol) 2328 - 5.10
Level 1, Nico Okarr (Ranged, 2 Pistols) 2542 - 5.10
Level 1, Paxton Rall (Ranged, 1 Pistol) 2392 - 5.10

2 mil heal parse, against 4 mobs in star fortress story mode:
Paxton Rall - 292 dps, 8461 heals, 7368 eff heals - 5.10
Riana Temple - 33 dps, 7514 heals, 6225 eff heals - 5.10
C8-S3C - 14 dps, 7265 heals, 6054 eff heals - 5.10

DPS - 1mil damage on the fleet operations dummy:
Level 50, Shae Vizla, 6700 (Ranged, 1 Pistol) -5.6
Level 50 Master Ranos, 5400 (Melee, 2 Sabers) -5.6
Level 50 Veeroa Denz, 5300 (Melee, 2 Sabers) -5.6
Level 50 Hemdil Tre, 5250 (Ranged, 2 Pistols) - 5.6
Level 50 Ensign Temple, 5200 (Ranged, 2 Pistols) -5.6
Level 50, Darth Hexid, 5100 (1 Dual Saber, Melee) -5.6
Level 50, Dr Lokin, 5100 (Melee, Custom attack) -5.5
Level 50 Kaliyo Djannis, 5030 (Ranged, Blaster Riffle) -5.5
Level 50 K1-Z3N, 5080 (Ranged, 1 Pistol, Special Skills) -5.5
Level 50, C8-S3C, 5000 (1 Vibrostaff, Melee) -5.6
Level 50, D-R3D (Melee, 2 Vibroswords) 5000 - 5.6
Leval 50, Lana, 4668 (1 saber, melee) -5.5
Leval 50, HK-51, 4230 (Ranged, Sniper Riffle) -5.5

Level 50 T4-1D Droid, 4700 (Ranged, Blaster Riffle)
Level 50, Yuun, 4500 (Melee, Vibrosword)
Leval 50, Gault, 5043 gault (Ranged, Sniper Riffle)

Leval 50, Theron Shan, 5180 (Ranged, 2 Pistols)
Leval 50, Vette, 5100 (Ranged, 2 Pistols)

Level 1, Shae Vizla (Ranged, 1 Pistol) 4160
Level 1, C2-N2 Droid (Ranged, 1 Pistol) 3260
Level 1, C8-S3C Droid (Melee, 1 Staff) 3356 - 5.5
Level 1, Darth Hexid (Melee, 1 Staff) 3280 - 5.6
Level 1, D-R3D (Melee, 2 Vibroswords) 3235 - 5.6

Heals/HPS - 1.5mil heals in story mode star fortress:
Level 1, K1-Z3N, 5560
Level 1, C2-N2, 5371
Level 1, T7-O1 ,5614
Level 1, TY-4N ,5491
Level 1, Broonmark ,5404
Level 1, Guss ,5656
Level 1, Skadge ,5490
Level 1, Shae Vizla ,5400
Level 1, K'lor'slug Soilder ,5300
Level 1, Ginx ,5525
Level 1, Treek ,3057 *
Level 1, Personal Warbot ,3196 *
Level 1, ISO-5R ,3974 *
Level 1, QO-77 ,4360 *
Level 50, Ensign Temple, 7448
Level 50, Kaliyo Djannis ,7378
Level 50, Master Ranos, 7171
Level 50, Veeroa Denz, 7596
Level 50, K1-Z3N, 7551

* Died a horrible and painful death before they could get anywhere near 500k heals in the same circumstances that other comps never died.

Known Bugs:

Force using companions (dark or light) only get a 4 second stun instead of a 5 second stun.

Force using companions Kill shot is channeled, when other types of companions have an instant kill shot.

All Ranged Tanks can shoot from 30.5m but fail to charge over 30m, which leaves them standing back and not using full tank rotation (the second damage reduction skill requires 4m).

HK-51 is the worst DPS companion in the game, that isn't from cartel. He also does not have real tank skills, he really can't tank more than a bit of trash. He also sometimes ends up stuck inside objects when he jumps back to you.

Treek's base damage and skills are not updated correctly for 4.0 and will perform at 30% less. She also lacks a Cooldown-less heal, which means she'll have trouble keeping up in hard fights.

T7-01 as Tank can't charge (it fails), so he can't use his full rotation and makes a very poor tank.

k’lor’slug soldier has minor nerf to crit and MAJOR nerf to DPS skills and base attacks. Will perform at less 60% less. I'm told this effects all creature cartel companions. It's also had some health problems...

T4-1D as Tank does not have a charge attack (its a special ranged one), so he'll never get within 4m to use his second damage reduction skill and as such sucks as a tank.

D-R3D has a broken AOE damage skill, it only ticks once which means he's not as high of dps as other 2 weapon companions.

Broken companion list (more convo and visual issues)