Possibly Watson, simply for his superior boxing skills. Although Froch is physically bigger than anybody Watson would ever have faced.
Ditto, Watson was a classically skilled boxer. Frochs only chances would be his size and strength advantages
Watson was physically strong as ****, and would push Froch back all night. This is a mismatch. Watson puts on a clinic and wins a wide UD. I would give Froch a shot a winning by come from behind KO, but honestly Froch doesnt have Eubank's power so I dont see it happening. Watson wins going away.