John Kasich almost has to be the guy, unless there is something hiding in the shadows. He is a Governor of a critical battleground state and won elections by good margins. He comes across as a "moderate" while actually being rather conservative. He has put forth seriously insane tax reforms that looks great in the short term to make him appear competent. He is mainstream, so he'd have the backing of the establishment, and while appearing "moderate", could get enough support from the whackos of the Republican Party. His strongest quality is his ability to keep his mouth shut regarding moral issues, and he never brings up rape. (That makes a Republican electable in the US)
He is what Scott Walker wishes he was. The only legit opponent is Jeb Bush, but I don't know if the country wants a monarchy. I could barely handle another Clinton. Forget a third Bush! Anyone else in that list likely loses by a landslide in '16. I think Kasich can win.