Gingrich is smart, but with a terribly weak record on personal morality--and I can't quite forget the commercial with Pelosi and Gingrich promoting the global warming nonsense.
Romney's personal morals seem to be pretty good, but if there is any serious and consistent ideology there, it hides well. The one thing I am sure of about Romney is that he wants to be president, very badly. At least if he defeats Obama, that's a good thing.
Santorum I can respect for his courage to confront America's loudest and most powerful whining faction, but that is also the reason that he could probably not win the general election. Unless you are at least neutral on homosexuality, you are unelectable.
Perry seemed like he had a lot going for him. I would love to see him suddenly overcome his verbal clumsiness and become an effective debater.
Paul's foreign policy ideas are delusional. I respect his courage in defending libertarian ideas in an antilibertarian nation, but that is part of why he could never win the general election against Obama.