Newt. His contract with America was a huge success. He could run on it again, and it'll fly.
The liberal press will attack him to no end, but his message is truth. They'll only bring more attention to it. The negative media will actually be a benefit to him. He could use it to it's full advantage.
Newt is actually my favorite at the moment, but he has two major problems.
There is a fickle segment of social conservatives who will not forgive him for his personal life and failed marriages. It doesn't matter whether they agree with him on 100% of the issues and his agenda. They will punish him for his personal past.
The other problem is that he's been very vocal and visible. As a commentator on television, he's built up a huge library of stuff he has said. It doesn't matter that he's been 98% correct on everything he's said. He's been outspoken and it's on the record. His opponents have a vast resource to pick through to find statements that, in hindsight, look bad.
So, like I said, I don't know how it will play out.