TOS: Spock or McCoy--Kirn was an arrogant womanizer in my opinion. This goes for both version of Kirk.
TNG: I used to like Picard, but now I flat-out despise him. He's just a holier-than-thou ideological mouthpiece. Of the TNG crew, I can't say I really LOVE any of the characters, but Data was pretty interesting.
DS9: Sisko I generally like a LOT. He gets edged out by Kira and Gul Dukat, but BARELY. He's the best captain of the bunch, though!
VOY: Ugh, Janeway. Not written as a consistent, competent commander at all. The Doctor is a more interesting character, I think.
ENT: Archer was badly, badly miscast. And I really hate saying that because I adored Scott Bakula, but I think the man is much better cast in "softer," more "emotional" roles like on Quantum Leap, or kids' movies (both of which I loved him in). He doesn't have sufficient gravitas to come off as a credible captain. As for the other characters of ENT...well, I checked out sometime in season 2, so I can't really say that anyone else stuck out. (If I rewatched Seasons 3 and 4, maybe I'd change my mind...dunno.)