I put Kos and Fitch about equal in terms of what they have done. Kos took more chances so he was KO'd by a guy like Paulo. And he took a Thiago Alves fight on 2 weeks notice and lost.
Fitch might have the better w/l record, but he also fought as safe as possible and hasn't finished anyone in years, and most were cans.
Bisping is below both. Not nearly as many quality wins. When he loses he gets destroyed. I'd put Bisping on a Diego Sanchez level.