This isn't who should he fight, it's who will he fight.

A couple notes:
I didn't include Winky because he said this was only a one-time thing at this weight.
I did not list Taylor because they have already fought twice, and there is usually very little interest in a third fight when one guy won both of the first two fights.
I didn't include the big heavyweights like Wlad/Peter, because they're not realistic options, there's just too big.