There's no one really. We'll see if anyone comes up by then. I'm still hoping for Romney, but I'm afraid the fabricated Romney created to destroy him is too much to overcome.
I don't think the flip flopping is as big of an issue as people think. Actually, given the trends in the base and country as a whole he may need to move further right on a few things (like guns) to be viable. That and do a better job addressing the whole Mormon issue than he did last time. With that said, I have a hunch he's going to be the compromise candidate given his run the last time plus his gains in the polls.