I really enjoyed playing as Agent and Assassin.
Sith warriors seem like the dumb brutes, who'd roar loud and mighty, but would get turned into cannon fodder because of their stupidity.
However, I found the Jedi Knight similar - something about him made it feel as if he's the brainwashed enforcer of the republic. If the republic would outlaw little kittens tomorrow, then the Jedi Knight would be the first to hunt down those kittens, lecture them about how good always prevails and then kill those kittens with 0 remorse.
I haven't finished the JK storyline though, so he could prove me wrong.