Corso = Single Target Tank
Bowdaar = AoE Tank
Risha = Single Target DPS
Akaavi = AoE DPS
GUSS = Healer
I would rephrase that significantly.
Corso = Single-target Ranged Tank
Bowdaar = Melee Tank
Risha = Ranged dps
Akaavi = Melee DPS
Guss = Healer and single-target CC
Risha is very good at sniping, but she's also good at AOEs. I built my dps smuggler as an AOE spec, and combined with Risha against weenies, from the first shot fired the smoke clears very fast. While Akaavi is also good at AOEs, the sheer AOE burnination of Risha and a specced smuggler is crazy. And fun to watch, too.
As far as Guss goes, he has a very strong single-target Crowd Control (or in this case, Creature Control, since it's single-target only). He can hold something for quite some time, but damage will break it. While a capable companion healer, he won't keep you alive under very heavy fire, but as a gunslinger, my survival rate went way up with Guss. He can reduce damage with his CC, and heal you during the cooldowns. Downtime is much lower with Guss out, but overall damage is also lower since your companion isn't doing as much dps, so combat is only faster if you're specced for AOEs yourself.
Akaavi is a weak tank, but can survive severe punishment for short periods by using her defense shield. She will activate it normally at 50% health if it's off cooldown. If you send her into a really nasty pull, you can manually activate it as she leaps in, and she'll last much longer. Because I can't heal, I generally have her damage increase ability toggled off so that it won't consume the shield's cooldown. People are often amazed at Akaavi's effectiveness combined with a scoundrel, because she can really dish out the punishment as long as she's receiving a lot of healing. One issue with Akaavi is that there are no +Aim hilts, thus you must replace and cannot upgrade weapons for her.
Bowdaar's Wookiee Toss is exaggerated. I have never had him toss something into another group. He uses it most often as a finishing blow which has tremendous style points, and the only issue I've seen is when he knocked a monster I wanted to loot off a cliff. Also note that his AOE taunt (wookiee roar?) does damage, so it will break most forms of CC. Don't bother using your Flash Grenade if he's roaring. Bowdaar is EXCELLENT at keeping things grouped up as a tank compared to Corso, making him the best tank choice for AOE specced 'slingers.
You should use the backtick (or whatever you mapped it to) to see the additional companion abilities. You'll need to do this to turn off Corso's harpoon shot, which is one of the most annoying things that turns on whenever you summon him, zone, or take an elevator. Right-click any ability to toggle it on or off. Use this to switch Risha into AOE mode or to turn on/off Bowdaar's wookiee toss.
I also mapped Attack and Follow to useful keys, as those are used often, and it works for all companions. Simply add it to the default of control-1 (attack) and control-2 (follow). The last thing you want is your companion to go off running through several groups of monsters due to a pathing issue... so being able to call him back IMMEDIATELY is important. Remember that Follow is a toggle for being passive, and stays on after resummoning. If you hear your companion say "I'll follow you" or "Right with you, Captain" or something like that when you summon, it's still turned on and they won't participate in battle until toggled off or specifically told to attack.