IA Sniper for me so far.
Awesome story keeps it interesting, the planet quests fit the character as well because being given quests by Imperials actually makes sense when you are an Imperial yourself and on top of that the DPS is out of this world (And get better the higher you level!).
I also really like the companions, though once you get Doc you never really need any others. On Belsavis so far (Level 40) and very much enjoying it