Personally, I think the best post-bacc is the one closest to you. I'm not convinced that intro science courses have that much variation in quality from school to school.
Then again, if flying across the country to attend a post-bacc because you feel that the school will give you a better education, I can't really fault you.
I myself feel a small amount of pride at being able to take courses at Harvard with the same curriculum and with Harvard faculty, and that feeling drives to work just a bit harder.
I know there's probably very little difference between taking pre-med courses at Harvard X and, say, UMass-Boston, but there is a certain mental aspect to this that drives me to do more; and whatever school makes you feel like you could succeed in getting into med school would probably be just as valid a choice.