Yes, which smp you choose matters. Even though they're all last ditch efforts (meaning doing bad in med school classes looks bad), I would still be a smart shopper. Which one seems more successful in getting people into the host school? into other med schools? Does which state you're from matter when applying to the smp's neighboring schools? Which one would have a higher chance allowing you to skip a gap year? Did you consider the potential of in state tuition for the 4 years of med? Which one have you heard more negative things about? In terms of prestige though, don't just go to a program just because X is the oldest one or Y is the smallest or Z had the highest success rate a couple years ago. Consider everything.