Yeah sorry I forgot to mention, it is for PhD programs and they are all funded. However, most are funded the first year and then the PI/lab will take over the funding. Likely, I will apply for NSF/alternative funding after the first year. At Michigan though, the fellowship guarantees funding for 5 years.
All in all, I think I have narrowed it down to Columbia and Michigan. While Michigan is ranked higher (it's 10th vs 20th for Columbia), I am more interested in the research project at Columbia. However, the lab at Columbia is small/cramped and the PI at Michigan is more recognized in the BME community. He has a lab of about 30 post-docs/PIs, which is a lot bigger than I am used to, but he seems really dedicated to interacting with his students individually. I am just concerned that with such a big lab, he won't be able to give me as much guidance as the PI at Columbia. I'm really grateful for these options, I just wish there was an obvious choice between the two!
Thanks for the advice!