I currently have a level 40 Guardian. I tried leveling as a Vigilance Spec then changed to almost full Defense tree with 5 points on Vigilance (http://www.torhead.com/skill-calc#500GzRrdbMRMzZcM.3). I'm also am now using Doc more than Kira - haven't died yet and basically just trying to get all the mobs in one place and do spam aoe damage. Having fun so far using Defense tree.