I vote Sousuke Sagara, because he's better at hiding than Spike, and thinks through his actions better, yet has a very similar reaction time to Spike--meaning he will make a better choice just as fast as Spike makes an okay one. And in the end, he has more of that hero luck. Spike is, after all, assumed to be dead at the end of CbBB. Revy is a third, with Rosso trailing.
I know this old but I just had to say who would actually win
Ladd Russo curbstomps all the others without much trouble.
Ladd can cut throats faster then the eye, defeated two bullet timers on one of whom has super strength, he took a hit that could make small craters in the ground and simply shrugged it off, and that stuff was only in the Anime.
His feats in the books go further his punches are described as bullet speed, he caved in a giant man's chest with one punch, he made an entire stone wall shake by swinging his prosthetic hand into it, defeated 3 of the world's top Assassins and broke their jaws and faces, the shot a guards ear off with his skill
His H2H skill may not outclass Spike persae but his boxing style is far faster then any of the others could see coming. Not to mention being a crack shot with his Lupara shotgun. Also he comes from a world were immortals and other supernatural creatures exist. Ladd basically outclasses them all I could only name likely around 9 people from his universe that could take him in straight up combat.