Christie is the most likely nominee/not likely to be the nominee.
This is probably true. With a potentially crowded field, there is no Republican with a better than even chance of being the nominee.
How many Republicans are even better than even to run? I'd say Santorum, Paul, maybe Cruz and that's it. I don't think any Republican is much higher than 10% to be nominee or will be until 2015.
I'd say Chris Christie, Marco Rubio, Bobby Jindal, Rand Paul, Paul Ryan and Rick Santorum are more likely than not to run
Rick Santorum is close to certain, barring health issues. Followed by Chris Christie and Bobby Jindal. And then Rand Paul at something like 75% likelihood of running.
Paul Ryan's numbers have taken a beating, although he handled himself well enough as a Veep candidate. And you don't agree to the spot unless you're really ambitious.
I don't see immigration as a major issue for Rubio, but there is the Jeb question. There's probably a 40% chance he decides to sit out 2016.
Cruz has been making some moves, and the far right likes him. But it isn't clear how he'll hold up to national scrutiny.