It's a fair question. In my opinion, it's Rick Perry. He isn't in the limelight much, save for some awful performances in debates, but with that set aside, as hard as it is to set aside, he has a directness that, when he uses it, makes him formidable when dealing with opponents. As much as he has looked like a joke in the few times he's showcased, he's the governer of Texas, where I live, and has a very impressive jobs record in the state, and thumbed his nose at the religious right with the HPV issue.
If it were up to me, he would be it, but there are a lot of conservatives who want anyone but him, but with Michelle Bachman and Herman Cain as the darlings, to name just two, he's far from the weakest of the bunch.