As I see it right now, without a doubt the most exciting fight would be him versus Floyd Mayweather, even Max Kellerman basically called Mayweather out before the Judah - Clottey fight saying that there is alot of people saying that Mayweather can't beat Margarito, I don't know if that is true or not but it would be a hell of a fight.
Oscar de la Hoya is also an option and could be the biggest moneymaker of all current welterweight contenders. I have a problem with this one though because who has de la Hoya really beaten lately, he is just relying on his reputation from nearly a decade ago and his name recognition. Regardless I think de la Hoya could end up taking on the lighter weight Manny Pac, and I also think the Manny could give him huge problems even at 140 to 147 lbs.
I believe the most deserving fighter would be Paul Williams, whom has already beaten Margarito and who has the best chance of beating him at Welterweight right now because of his height and reach.
A couple others that could be mentioned is a rematach with Cotto, which I think Cotto would want to get another one or two fights in before getting back in the ring and even then after what we seen the other night I wouldn't think it would bode well for him.
Also, Joshua Clottey could be another one that fits the bill he did go the distance with Margarito which is more than what an undefeated Cotto did.