MOsley vs JMM today at 147?
Mosley! The weight advantage will be to much. Skill vs skills, JMM will win that "argument". But Mosley is to smart to not us his advantage on a much smaller opponent. Besides Mosley has a good chin. Always did. And if Diaz can't stand for 8 or 9 rounds, Mosley can't have that puncher chance, even if he gets outbox for 12 rounds. And we all know that JMM gets hit and touch the canvas quite a few times.

Mosley vs JMM in the prime at any weight(catchweight) 140?
Mosley! JMM skills is superb but Mosley in his prime was a beast himself. Mosley in his prime was KOing people like that was the only way to win. Mosley KO percentage in his first 40 fights(before Forrest) was like 90%. JMM would have just been another victim.

Better fight for Pacman?
Tough to choose. Cause right now, at any weight, Manny would ko JMM. Just the simply knock downs would change to KNOCKED OUT! That's at 140 or even worst, 147. Not saying that it would be any easy fight. JMM maybe the only fighter that use counter punching against Manny effectively. Effectively cause Cotto was on the run and in survival mode. And IMO, that's the style thats gives Manny more trouble then a striaght forward fighter. On the other hand, Mosley chin can stand longer then JMM. And Mosley was and always will be willing to trade punches if someone is willing to trade with him. Problem is, Manny don't trade. Manny hit, cut and angle, bounce in and out, regroup and repeat. But he gives his opponents a chance to hit him if they are willing to get hit. Mosley is that fighter! And if Mosley hit Manny, and Manny tap his gloves and throw his arms in the air, get ready for Mosley to get the ko with a trading Manny that want to get his hit back.
BTW Mosley by KO rd 8 or 9