Which GOP 2012 candidate seems to stand the best chance against Obama?

This question is an attempt to create some political thought. This isn't to say that President Obama is going to run away with the 2012 election. But as many may know, the 2012 GOPers seem relatively weak and have major flaws. Mitt Romney has been attacked by the GOP for his ping of health care reform in MA. Rick Santorum is known as a conservative social extremist and is unknown on the national scale. Gingrich has spent the past couple days having to defend himself, and is producing more negative headlines then any other 2012 candidate (especially with that statement against Rep. Paul and the budget.) So who of the 2012 GOP candidates stands a good chance of getting some independent votes and not being "too extremely conservative," as well as not neglecting the all important conservative base?