Romney. They aren't going to give it to someone who hasn't spent time in the primaries. Little chance that they'd give it to Newt, and zero chance that they'd give it to Santorum or Paul.
They'll give it to Romney, and force him to pick someone as Veep who they think will mollify "the base" in exchange for the base going along with the mess.
Prepare to be told that Romney and _______ (insert marginally acceptable Veep candidate here) is the best they could do and that we should be thrilled with the situation.
Further, be prepared to be beat about the head and neck with calls for "party unity" in exchange for (maybe) a nod or two to conservatives when the platform is written.
there is no one that Romney could pick that would make me more likely to vote for him.