Three deserve consideration in my opinion, even though they all have drawbacks.
Romney- Has business experience and executive branch experience. Successful in buying and turning around failing companies (sounds a bit like our country right now). Obvious drawbacks are the more liberal social programs that he pushed, or tolerated, in Mass. The one big question with Mitt, for me, is "How much of his Mass. negatives go to his being a pragmatist? Was it a way to get more conservative agenda items passed?"
Newt- The only balanced budget in 40-some years was passed under his congress. He is the best debater, hands down. He does have a history of leaning left on some key issues including global warming, which was propped up with faulty science. Where is Newt on these issues, now? Where will he be in 2 or 4 years? No executive experience.
Paul- For fair disclosure, I donated to Paul in 2008. I love a lot of what Paul stands for. Small government is great, liberty is great. Isolationist foreign policy and allowing Iran to wipe Israel off the face of the earth with the Nukes they are currently developing, not a fan. Can Paul become more of a pragmatist and get some of his agenda items passed? I really don't think he can take 50 cents if he wants a dollar, even if that 50 cents gets him closer to a dollar. No executive experience.
The other one left is Santorum,
I cannot and will not vote for a Big Government Social Conservative. I am for smaller government and it's not the government's job to regulate morality.