My take on these four
Sarah Palin... She might be a great figurehead for the tea party bunch and would probably be content to do as she was told on policy so long as she can play President around the world. She apparently has the charisma, but she's too much of a loose canon for the business side and has no appeal to independents and moderates, something that will be required for the general election.
Mike Huckabee... I'm not sure how a religious conservative plays to the libertarian side of the party, plus Huck is fairly centrist on some issues and that won't play well in the primaries. On social issues, he is very Christian and that generally means very liberal. I also don't think he would be all that business friendly. Not that he'd get my vote, but he'd be an interesting President.
Newt Gingrich... Newt is an awesome political beast and shouldn't be discounted. He's very pragmatic and I can't see him sacrificing the country's business to promote his agenda. He comes from a time where both parties actually worked together on occasion and that might work against him. Still, he is one of the most calculating and shrewdest guys in the running and will play well with the libertarians and the business types while not inflaming the religious voters. I think his biggest liability is his lack of name recognition for the under 40 set.
Mitt Romney.. At heart, Mitt is a pro-business moderate. He's been moving right to boost his primary cred, but the more extreme primary voter from both the libertarian side and the religious side is not going to buy it. I think he will wrap up the pro-business Republicans, but that's not enough.