Mitt Romney: 19%Unless Rs vote in Iowa the way the Iowan Ds did in 2004, choosing Kerry based on his electability, over Howard Dean, who I'm sure they liked more, I don't see the Rs nominating any of the top candidates above.
Jeb Bush: 14%
Chris Christie: 9%
Mike Huckabee: 9%
Ben Carson: 8%
Rand Paul: 5%
Ted Cruz: 4%
Rick Perry: 4%
Paul Ryan: 3%
Rick Santorum: 3%
Marco Rubio: 3%
Scott Walker: 3%
John Kasich: 2%
Bobby Jindal: 1%
Carly Fiorina: 1%
I think there are only a handful of serious possibilities of getting nominated above, but foremost is Paul Ryan. I see him as the favorite and I also think he can beat Hilary.
Other serious possible R nominees:
Romney - maybe, but not exciting enough as a candidate, not to mention as a person
Bush and Christie - their unfavorables are too high among R voters
Rand Paul - maybe, but too far outside the mainstream with some of his comments. And unless he can skirt Kentucky law that doesn't allow anyone to run for President and Senate at the same time, I don't even think he'll run for 4 more years.
And the dark horse of those not even listed here: Mike Pence from Indiana. Also, a good VP candidate.
My biggest concern is Hilary's health over the next 23 months. If she has an episode of any sort, I don't see a single D who would come within 15 points of the R nominee unless Elizabeth Warren changes her mind.