I just want to step in here with a slightly different single target opener for guardian.
Firstly, please don't use saber throw. It just doesn't generate enough threat to make the extra 3 focus (which is slightly unneeded if you are maintanking) worth it.
1. Combat Focus
2. Leap + Reflect
3. Guardian Strike + Riposte
4. Hilt Strike
6. Blade Storm
7. Master Strike (The taunt is to ensure you don't lose aggro during MS which is just a pain)
Then just proceed with normal priorities (Just a side note, your dps do have aggro drops and should be using them when they see the taunt as avisual cue, except for sentinels and guardians due to the inherent usefulness of their threat drops)
The idea behind this is that your dps don't do amazing dps while they are dead, and also if they have to move during their opener or interrupt a cast in order to threat drop it's just detrimental.
So this opener brings the balance between allowing your dps to maximise their dps and you holding threat.
Discussing a few items, the first one being, Why is Sweep so far down the list?
Sweep is so far down the list because I have ordered the opener in terms of Highest Threat per GCD to Lowest Threat Per GCD, and Sweep just doesn't generate as much threat as Hilt Strike, so why put it before Hilt Strike? Because of the Accuracy Debuff + Armor Debuff I hear you say. Well the Accuracy Debuff is applied 1 GCD later, so unless if you get railed by an unmitigated M/R attack that would have missed if you had that extra 5% effective defense and your healers are unable to compensate for that hit in the first 4 GCD's of a fight, then by all means throw that sweep up 2 GCD's earlier, but outside of that extremely unlikely scenario, place it in it's proper place, which is below the higher threat generation moves. The second part of Sweep gives the boss an Armor Debuff which helps your personal dps and the dps in your group hit harder, and this is where this opener creates the compromise that allows you to hold threat. The Armor Debuff helps out the dps in your raid team a whole lot more than it does you, this basically means that you have a harder time holding that threat because the dps are already hitting much harder than you, on the flipside, the dps are usually number hungry wolves who are insistent that the boss should be their new friend and not yours, and will be disappointed at not seeing such high numbers between GCD's 2 - 4, but they can suck it up, because they get to live. Again this is pretty much personal preference, because the difference between a non crit Hilt Strike and a non crit Force Sweep is about ~400 threat, but it's still more threat, and it is effectively ~520 threat to the dps that are trying their damnedest to pull off you. Once crits come into play, it only widens the gap.
Why don't you put Sweep before Guardian Slash?
Guardian Slash gets turned into an approximate conal attack when used on a target effected by an Armor Debuff, which is all brilliant, except when you are pulling a boss that doesn't have adds up straight away that are within the reach of the conal, it only buffs the damage by Guardian Slash by a little bit from the Armor Debuff and as I said before, buffs the dps in your raid's damage much more. Guardian Slash is the highest threat move you have available to use because it has a 2.6x threat multiplier coupled with it's fairly high base damage and allows the use of Riposte which hits fairly hard as well as being off the GCD. More importantly, using Force Sweep before Guardian Slash delays your snap threat which can be vitally important if you have an aggro hungry gunnery commando in your raid who gave up long ago on starting with TO +GR > Relic + Adrenal + DR > HiB because it was just a recipe for disaster if he got some crits or if I had a miss/resist on any of my attacks.
As a side note, this opener slightly reduces mitigation for the first 7.5 seconds, but at that point in time it shouldn't be that much of an issue provided your healers are well, healing.
TL;DR, If there is one thing you should take away from this, don't use Saber Throw if you are MTing, you will get enough focus from Combat Focus and Leap to go through the first couple of GCD's without issue, Saber Throw is a wasted GCD due to it's pitiful threat generation and is just a recipe for you to lose aggro.
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This is intended to be your opener if the dps in your group are pre-casting and are leaping/attacking as you leap. If they aren't, they should be.