If Williams fights like he did from the outside against Margarito, throwing close to 100 punches a round, mainly jabs, he's my pick. I think Williams rarely takes advantage of his reach... If not Pavlik is, based on his similar high work rate and the fact that he wouldn't be affected by any leather coming his way. He would just absorb all until he lands his bombs..
Both guys are too big for Floyd Mayweather in my opinion. If either one beat PBF, they'd say it was because of size...and they'd be right.
But would he ever consider fighting either? I'd settle for Williams, but even fighting a big middle like Pavlik , one dimensional as he may be, would be quite a chore. I'd love to see these fights, and I figure Floyd would win , probably Pavlik being easier. But Floyd will never go for it. if he can get millions for fighting smaller guys, why would he look for a tough fight?