Prime.
He has shown, time and time again, that he is more than capable of dealing with entire groups of heralds simultaneously.... And at less than full power to boot. That aside, I'm also skeptical to assume Marv's blasts would be able to cause any significant harm to Prime for a few reasons: a.) his energies seemed to have a magical/mystical/arcane overtone to them, and Prime eats those kind of energies for breakfast -- b.) even Anti-Monitor's anti-matter energies were completely ineffectual against Prime... Can't imagine Marv's blasts packing more of a wallop then that.
My opinion.