Skill wise it's Charles all the way. Physical strength obviously Bruno. Can Charles survive the slamming punch s from Bruno and take him deep, where Frank became less successful? Charles had heart, he won't become discouraged I believe. But still a physically hard challenge for him.
What version of Charles are we talking about? I find heavyweight Charles to be more of a risk taker and, at times, pretty wide open and desperate. Not that Bruno was great at capitalizing on openings but that jab is enough to do a lot of damage the sort that Charles did not often experience.
I would pick Charles, but not with a whole lot of confidence. He's clearly vastly superior in an ATG p4p sense, but it would still be a tough fight for him considering what he'd be up against.