Assassin/Shadow or Powertech/Vanguard, since they are both great DPS and have tank specs. Marauder/Sentinel if you want to just play as DPS.
If you must do ranged, then Sniper/Sharpshooter. Mercenary/Commando is currently trash, Sage/Sorc are average.
What do I play? In 1.0 I was a PT, and remained so until 3.0. After that I was a Merc. Now, I'm going back to PT.