I went to Columbia for post-bacc and had a really great experience. The classes are very tough - those Columbia undergrads are pretty bright! - and the advising system was really what you made of it. A lot of people complained that they weren't being supported, but they also never made any effort. Also, a LOT of people dropped out after the first year b/c their hearts weren't in it, didn't think it would be so hard, etc.
I had a friend who went to NYU who really enjoyed it b/c of their accelerated program - she did everything in about a year, where it took me two years to complete the program at Columbia (although, Columbia may have a more accelerated system in place). We both ended up at the same medical school at the end of the day.
Honestly, I don't think medical schools are wowed by the Columbia/Ivy League factor. I would give each school one last look and just go where you feel more comfortable - do you like upper or lower Manhattan better? As someone on the admissions committee for UPenn School of Medicine, and a previous post-bacc, I can without a doubt tell you that the only thing that matters is doing well in your postbacc - wherever you end up.
Good luck!
