Please discuss. And not just fighting ability alone, factor in things like intelligence, speed, etc. And looks Just kidding! Though I do have to admit, that seems to be a significant factor.
I know there was a thread about this a year ago, that's the only thing I could find when I searched.
Poll should be coming.
EDIT: Personally, I would choose Mihawk. It's obvious bullets wouldn't be effective, since he deflects them with ease. With that enormous sword, he sliced up 50 entire ships of Don Krieg's armada. And he could still fight without it, see his duel with Zoro. He used a knife that had a blade of maybe 1 inch? There's only a few people on that list who would have the ability to sail halfway around the world (well, from the Grand Line to the East Blue) on a dingy raft, and still be able to cut down bloodthirsty pirates.
Of course, knowing Mihawk, he'll actually want somebody to surpass him. But for me, that's not large enough of a factor.