Sisko, because he does a little bit of everything, because he has the best backstory of any Star Trek captain, and of course, because he's the emissary. And also because he's the only Star Trek captain who dies at the end (unless you count Janeway in the alternate future). I cried my eyes out during that scene.
Janeway's a good leader who knows what she's doing, so I'd have to say she's about tied with Picard, except that unlike Picard she knows exactly -when- to follow the rules and when -not- to follow the rules. She takes advantage of the situation in a way that will protect her crew.
Picard's a good captain too, but he's more of a commanding, traditional authority figure who really doesn't have all that many unusual traits or interesting bits of backstory to make him really interesting.
As for Kirk, the way I see it people only like him because he was "the original". Well, actualy, Pike was the original (Why isn't he listed in the poll? Or Archer, ftm?), but that's btp. Kirk just comes across as too much of a jerk for my tastes. He's just too macho for me to see him as a likeable captain.