Most powerful: Sith Warrior.
I'd point out that the only reason the Emperor is as powerful as he is or has his position is because of supernatural power and rituals
However he obtained that power, the fact remains that the Inquisitor took his position on the Dark Council via his own power, whereas the Wrath was effectively appointed by the Emperor.
And given that Act 3 pretty much serves as warning that bad things happen if you falsely invoke the Emperor's name to advance your agenda, that Wrath can't even really make use of his power without direction from the Emperor or the Hand. Whereas the Inquisitor can do pretty much do whatever the hell he wants.
Both JK and JC don't match up. The Jedi Knight is just annoying, and so badly written. Almost like a deus-ex-machina for the Republic. They are only class that actually does anything, and what they do is just... meh. Almost like Luke post-films, they're just a tool for lazy writing on Republic side. They couldn't think of a good way to make the Republic win, so they just bring in the Knight to 'win' in every sense.
I agree heartily about the JK. I can't even really get into the story just because they lay it on so fast and so thick. I just kind of rolled my eyes when after my first class mission I had the Grand Master of the Order and the entire Jedi Council tripping over themselves to tell me how awesome I was.