Oscar was a bigger challenge than any of those and Floyd came out on top.
Williams and Margarito, I'm still not completely sold on them yet... lets see how their fight goes.
Cotto is a class act who is improving all the time, but I think Floyd is a step too far for him right now.
Hatton didn't really cut it at welterweight and I can't see Floyd moving back to 140lbs just to fight him... if he did, I have no doubt he would beat Ricky pretty handily.
Mosley has looked good lately, but not against fighters as skilled as Floyd... I'm not sure he could handle Mayweather at this point. It would probably be the best and hardest fight to call from that list though.