I'm level 44 and Assassin is still pretty damn good. My single target dps is very good, on world bosses I can pull aggro if I mess up my stealth rotation, but if you are in stealth you shouldn't pull the boss around. It is a problem on bosses where players are launching them into the air. It can really mess up your stealth rotation, and when the boss comes down, he might come after you because he can finally see your sneaky ass. If you want some aoe, lightning rod and poison breath is pretty good, left hand branch is very strong, I can kill groups of mobs with it, and if they aren't dead you have 5 stacks of poison, which means you can do the super quick heart stab + R animation cancel with the 5 stacks up. During this moment when you are out of stealth you can actually do more dps than in stealth but it is very temporary. Only problem with poison breath left branch is the cd. The middle path of lightning rod hits hard and is aoe, with a 12s cd, but it doesn't stun anymore. If you want to regain focus on stealth and intend to stay there for pve, the right branch is what you want.