I've heard it said that no one could be worse than Bush. The reason we got Bush in the first place was because he had name recognition that other Republican candidates didn't have, and after eight years of Clinton, the Republicans just wanted to win regardless of ideology. We got a bad deal out of that, and it looks like we will get a terrible deal now.
All of the remaining candidates will be worse than Bush. The Wilsonian foreign policy will continue. Spending will continue. Once in office, a democrat will enjoy the new powers the Patriot Act and other post 9/11 presidential power grabs have wrought. Think about it. Everything you don't like about Bush's presidency, regardless of your ideology, will continue. Then add on top of that the inclinations of your candidate.