There seems to be some rumblings in Tennessee of a Carr upset and the Alexander campaign hasn't been too active. The answer even a few months ago would obviously be Roberts as it is a more high-profile race, but Roberts has ran a strong campaign, quickly defining Wolf. The X-Ray scandal continues to haunt Wolf as well, and almost all of his support, both in terms of cash and volunteers, is coming from out-of-state.
I have a bit of experience witnissing longtime GOP incumbments getting primaried (
Lugar) - that being said, Wolf isn't anywhere near the level that Mourdock was at, and Roberts has ran a much better campaign than Lugar has - nothing is sticking for Wolf. I'm going with Carr mainly just because I see Wolf's chances of winning to be extremely low. I would be surprised if he hit 40%.