This is an awesome thread as I'm about to make a tank. Now if I can only decide between shadow and sin.
Which faction is stronger for PVE endgame? That should probably be the deciding factor.
From a looks perspective, lightning > little rocks. Conversely, nearly all endgame Assassin PVE and PVP gear looks awful. Luckily, however, you can get 4 piece set bonus without using body slot (and put something better looking on), hide headslot, and then you're left with inoffensive hands/feet and a silly skirt until you're at a point where you can customize your look however you see fit.