I'd favour Groves but Froch could once again do what he has done previously and take over late and stop Groves. Groves should forget about trying to KO Froch he'll find himself eventually coming off 2nd best, Froch is just too tough. If he boxes, moves and doesn't trade then he can win on points.
I think that should there be a rematch it'll end in Groves being more cautious and potshotting his way to a victory without being drawn into a fight (that or a potential blitz). This is what is pissing me off so much about that **** Howard Foster's awful decision. It robbed us off a definitive ending (either Groves surviving the round and probably going on to win via decision or a resurgent Froch stopping him in the remaining 1:27 of the round). Now everything is tainted and if there's a rematch it probably won't be anywhere near as fun as before.