A guy who use his jab as his primary weapon will always win these kinds of poll. Look at a guy like Dzinziruk, he's got a great jab but was getting outjabbed against Martinez. You'll see the same thing when Cotto meets Mayweather... He was beaten to the punch by Pac's left hand ! Mayweather's got a beautiful jab to the body. Hopkins's got a great arsenal of jabs... Very hard to predict what he'll throw. At heavyweight, W. Klitschko is the only answer.
Khan Antonio Tarver deserves a mention Cotto has a very well educated jab, timing compensates for speed here.
Overall: Floyd Jr... It's so quick, and sometimes he throws sneaky right-hand leads in it's place, which effects an opponent's expectations of the jab. At Heavyweight: Wlad, easy. Cruiserweight and below (other than Floyd): Probably a tie between Donaire, Broner, and Gamboa. Underrated Jab: James Kirkland