So Floyd fights: Horn Bradley Jr. Algieri Thurman while Manny fights: Ortiz Guerrero Berto Maidana Who they defeat and who they lose to? Who causes them the most problems if any?
Both fighters would do a clean sweep over that list of opponents Maybe Horn with his rough aggressive style could cause Mayweather a few issues early on, and Bradley could probably steal a few rounds off Mayweather and lose a decision in the region of 117-111, 116-112. I don't really see anyone troubling Pacquiao amongst his list of opposition except for maybe Maidana, but I think Pacquiao's speed and movement would befuddle him like Khan did without the late rounds drama.
I think Floyd would be getting an overall tougher set of opponents than Pac would. I'd be curious to see how he handles Bradley & Thurman, who are the 2 best out of the total 8 IMO. I do think Floyd deals with Horn easier than Pac did, though.
Floyd is an obvious sweep. Ortiz and a faded Berto would've folded to Manny. Guerrero used to sit back and box until Floyd beat him and he turned into a slugger. He was much better as a rangy boxer. Compare his fights against Katsidis and Casamayor to Marquez's and it should be obvious that he'd at least have a chance against Manny. Maidana would have a chance if Horn could beat Pac.