Burst Classes > All
Assassins/Shadows Operative/Scoundrel Sniper/Gunslinger
If you wanna win PVP, play one of those... they are almost entirely broken when in full PvP gear.
However, that's just right now... But I'll tell you, in ALL PVP MMORPGS
Burst > Anything Else
Those class mechanics will not change, so pick a burst class and stick with it.