Hardest no because he isnt nearly as big and strong as Carwin. P4P hes right up there he has dynamite in those hands.
Carwin can bang. I'd say Mercer though, he might be touching 50 but he'd take anyones head off wearing those mitts.
He has by far the best speed to power ratio probably outright or p4p. Belfort has the sort of punch that brings about sleepy time no matter when or how it lands. Franklin, Silva, Lindland etc know the score.