One thing to consider with formal post-baccs is that it's another application process/cycle that may put off your med school education for another year. Don't quote me on this, but i think it requires recommendations, essays, etc etc. The benefit is the advising, structure, and sometimes linkage programs.
Personally, I thought that was a waste of my time and money. I'm not getting any younger, my opportunity cost increases with time. I didn't want to pack and move for a non-degree. With an a la carte post-bacc, I started classes right away while working full-time. When the time came, I quit my job, took a really heavy load full-time (fall, winter, spring) and finished all but one of my prereqs within one academic calendar. I was in control of when and where I take classes, and found a strong support network at my local community colleges (in California). Such acceleration can be difficult to pull off in a formal program which often don't offer all the necessary winter/summer classes at the right times to complement your needs.
Again, I'm just generalizing. You should definitely do your own research. There's Georgetown, Columbia, Hunter, Scripps, Harvard Extension's HC track, and many other very good programs. Do what best fits your unique circumstances.
Good luck!