That was my question, too, but since you're talking about a straight swap, I wouldn't vote for either.
McCain is far enough away from my beliefs that I couldn't support him as president regardless his VP, and picking Palin as a VP would be enough to scare me away from Obama. Not necessarily because I'd be concerned she'd suddenly be running the country, but because I'd have real difficulties supporting such an obvious stunt as picking a MILF running mate with beliefs/policies diametrically opposed to your own.