Based on polls conducted so far this year, here is Nate's ranking.
Nate describes two ways of merging numerous polls together in his article, which I will leave for you to read here.
Nate's caveat must be noted.
The value of an approach like this is not that these models are infallible. Instead, they’re a pretty rough cut, as revealed by the fact that relatively small changes in methodology can produce large shifts in the chances attributed to candidates like Mr. Trump or Mr. Pawlenty.
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(Stated far more technically, the polls are useful enough to serve as good Bayesian priors).
Intrade (the right-most column) is essentially a betting system. The more likely people think that an event is, the higher the price to bet on that event occurring. By looking at Nate's modeled numbers versus Intrade, you can get a sense of what bettors think about "intangibles" - the things NOT in the polls. The Intrade folks, for example, probably don't think Mike Huckabee is even running. And they think Mitch Daniels or John Huntsman can make a real play for the nomination.
This is also the most wide-open Republican nomination in decades.
The current Republican race is, by some margin, the most wide-open in the modern era on the G.O.P. side, but there are a couple of comparable examples if you look at the Democrats. The model would have had Scoop Jackson as the nominal favorite to win the Democratic nomination in 1976 — but still would have given him only a 20 percent chance. Michael Dukakis in 1988 (26 percent chance of winning) and John Kerry in 2004 (29 percent) were in the same range as Mr. Romney is now, though for different reasons — their polling wasn’t quite as strong as Mr. Romney’s, but they were doing it with considerably lower name recognition.
1976 was the year Jimmy Carter surprised everyone by busting his ass in Iowa and vaulting himself into contention by winning the caucuses. That was a game-changer and is the reason no one skips Iowa now a days (except brilliant strategists like Rudy Giuliani).