A significant number of Republicans will not vote for Giuliani, Romney, Huckabee or McCain, as evidenced by the level of passionate comments against these candidates in the blogosphere. Whether its 5% or 25% of total Republican votes, it will be enough to lose.
However, if Thompson is the nominee, all Republicans will vote for him, because he has no significant policy or ideological negatives. Thompson will unite the party like Reagan did, even bringing in many Reagan Democrats.
Fred is the best shot we have at keeping the White House.
Romney would be the logical pick as he provides geographic and idealogical balance. He could also provide fundraising, maximizing the amount of limited party funds available to help down ticket candidates. He is also second with positives at 73%.
My first choice would be a Hunter-Thompson ticket but, at this point, I don't see how it could happen.