My experience is that the bulk of individual postbacc success is driven by applicants and not programs - Bryn Mawr is the best postbacc program by far, but that's also because they are the most selective about who is admitted. Being a one year program with the most linkages, they get the best students. If you were admitted to Bryn Mawr, you have good test taking ability/personal statement writing ability/cohesive extracurriculars. The majority of medical school admissions committees are not wooed by the prestige of a postbacc (beyond a few that have a very strong relationship, like LKSOM and Temple), and good students will achieve strong MCAT scores wherever given that the majority of MCAT prep is self-paced. My friends at Bryn Mawr were very happy with their experience, but I also think that they would have been just as successful if they had done a DIY postbacc. If you prefer CU Boulder and see yourself doing better there, then I don't think that it is a mistake to attend.