Carson is a horrible candidate. It is amazing he's at the top of the polls. He won't win of course because the guy is absolutely insane. You can be brilliant in one aspect of life and be a complete moron in the rest. Carson would have zero chance of winning the presidency. He has zero charisma, zero experience, zero plans of action and is absolutely terrible in debates. He's going to fade dramatically. Marco Rubio is going to win the republican nomination out of sheer process of elimination. Trump has peeked and his popularity has declined in recent weeks. He has carved out a niche in the republican base but he isn't going to get much more than that. Carson is an evangelical crazy person who will start to crash very soon. He might win Iowa but Iowa also went for Rick Santorum in 2012 and Huckabee in 2008. It's not real indicative of the rest of the country.
Jeb Bush is a mess even with all the money he has, Kasich and Christie are moderates but too far back in the polls, Ted Cruz is a teabagger who can't break out from his base and he is a completely unlikeable human being. Paul is too far back and Fiorina's popularity has waned since that 2nd debate. Once Jeb calls it quits all his donors will go to Rubio and Rubio will have too much cash. He also is young, latino, and has charisma. I don't agree with practically all of his policy plans but on the campaign trail you win with poetry and once you govern you govern with prose. Rubio will get the nod and if Kasich's campaign hasn't ruffled too many feathers he'll be the VP. He's a moderate who doesn't piss people off. He has governor experience and he is popular in a swing state that is a must have to win the election. He also could help get moderates to vote for Rubio, who has a lot of policies that fall far right.