Marquez. Followed by *DLH, Corley, Ndou, Augustus, Chavez, Hernandez, Pep and Cotto in no particular order. He's also fought a lot of walking vegetables. Ortiz comes to mind, as does the one-note zombie version of Mosley (who never was brilliant, except in his prime the speed made that easy to overlook). Even Gatti and Corrales while not idiots were completely mismatched against Mayweather in ring IQ.
Marquez. Unfortunately his style doesn't (probably still wouldn't) allow him to express said intelligence in this match up. Although there was 1 or 2 eye catching moments of Marquez unlocking Mayweather's guard.
Definitely Marquez, followed by Chop Chop, then DLH. Marquez, like has been stated before, didn't get a chance due to styles to show off his Ring I.Q. Corley kind of did when he landed a big shot that hurt Mayweather.
I'm actually going to throw an asterisk next to Oscar. * In general, he was an intelligent boxer throughout his career...but he made a couple of epically stupid blunders that cost him on the big stage. (on the bike against Trinidad, and inexplicably abandoning the jab halfway through The World Awaits)
Correct. You wonder what he was thinking in there sometimes. The Mayweather fight is a good example. Not saying he would have gone on to win, but I had him 4-3 up after 7 rounds. He was doing well then changed his approach. Odd.