Vigilance | Vengeance 

Last for 12", this ability gives us a 50% chance to dodge Melee/Ranged damage and a 25% Damage reduction to Force/Tech attacks.  It is on a 3-minute cooldown.  It's a strong defensive, but its long cooldown means you will most likely only get to use it once in a fight.  I save it for emergencies, mostly.

More than likely our best Defensive ability, a 60% AoE DR for 15" on a relatively short cool down (45").  Note that Stalwart Defensives skill point must be chosen at level 64 for this ability to gain this utility.  I consider it pretty much mandatory for Hard Mode + Ops.

So, this one can be tricky.  As far as defensives go, this one does nothing for you.  It can however be used to help save a teammate.  NEVER use this on a tank, it will reduce the threat of the target of your leap.  Making the tank loose threat can wipe your team.  I have found this ability uniquely helpful in Izax (induction cascade).  I can quickly leap to the player getting pounded by induction, then run out before I take any damage or spread it (hard mode).  There are a ton of other uses, but you must weigh in using a GCD to help the healers or continue DPS to push the fight along.  25% DR to the target.

Enure is both a self-heal, a cleanse and a defensive.  The Self-heal is commonly referred to as "fake health".  You get an increase of 30% HP for 10".  Meaning, if you are already at 100% you can in fact push your health to 130%.  This can come in handy for a fight that does percentage-based HP damage (tyth rage overload).  As Vigilance, enure also provides us a 15% DR for 10".  The DR is handy, but usually enure is reserved for a cleanse in many fights, making it hard to use as a defensive cool down.

Short Cooldown (1 minute), for 5 seconds you reflect all single target ranged, force and tech attacks back to the attacker.  (Note NOT melee).  This means you take 0 damage (unless it's melee or AoE), and you reflect boss or add damage back to them.  Can be VERY powerful, and what the game considers single target can be a bit off from what one might think.  The spires on EC tanks for example are Single Target.  When I am new to a fight, I typically just step in whatever stupid I can find to see if reflect works.  This is typically my default choice.  The Difficulty with using Saber Reflect in a dps spec is that often the boss/damage is not targeting you.  In any fights where you know you will take some form of saber reflectable damage, this is the pick.

This movement ability dashes you forward 20 meters damaging enemies in your path.  It can be used as a defensive cool down for its 100% defense chance while blitzing forward.  Blade blitz can help you ignore some very high damaging attacks like DOOM in dread guards, or the titan 6 launch blast wave.  There's a ton of uses.  Like with saber reflect, I tend to try it out against different attacks to see where it can be used best.  Mastering the forward role takes some practice, especially if cliffs are close by.  35" cool down.  If saber reflect does nothing for me in a fight, this is typically my top choice as a DPS spec.

We first think of Awe for its AOE Stun ability against weak targets.  Against boss's though, it's just as powerful as it debuffs the boss with a 15% reduction to its melee and ranged attacks for 10".  Also, on a short cool down (1 minute) it can effectively give your entire team a 15% defense chance.  Helpful for phases of team wide damage and can be useful against add heavy fights where the adds can be stunned and reducing their damage will help (corruptor zero).  It's a great ability, but Blade Blitz and Saber Reflect often trump it.  As such, I only take it in fights where I cannot reflect and have no need to use blade blitz for movement.

This one can make us seemingly immortal.  First off it has 0 defensive utility, it will NOT reduce the damage you take.  This ability grants you 12 charges (and you must be below 70% HP to use it).  You have 15", during which time if/when you take damage a charge is consumed, and you are healed for about 25k HP per charge.  This means that if you are taking a low amount of damage, you can effectively heal up for ~ 300k HP in 15 seconds, a true lifesaver.  But if you are standing in something that is dealing damage to you at a rate of 50k/second, you are going to DIE!  You do not become invincible when using this.  I have heard so many guardians say, "I was using focused defenses, how did it kill me through that".  Read your tool tips people ;)