Thanks so much for everyone's input.
In reply to some of the questions:
I am interested in pursuing research but focused on clinical/public health in developing countries versus bench/translational research. All three schools require the equivalent of a thesis but I got the sense that Stanford is the most pro-research of the three.
I'm thinking of doing a MD/MBA with a focus on global health and non-profit management (which Yale currently has the top program in), but Stanford also has a great program with a strong entrepreneurial atmosphere.
As far as money goes, Yale and Columbia have offered the best financial aid (even considering the merit scholarships, with the exception of Pitt). However, Stanford through the Med Scholars program and TA appointments can also provide the lowest graduating debt (but that requires actively engaging in research throughout the academic year)
Is anyone else choosing between these schools? Once again thank you for everyone's comments and I hope that I do not come off as ungrateful for my success or choosing solely based on rankings since it just happened that these three schools are the ones offering the best financial aid.
Have you talked to Stanford about your aid packages? Given that all of these schools are private and you are obviously a desirable applicant, I would bet Stanford might be willing to match Yale/Columbia. If you don't want to go there, that's fine, but it seems like you've worked hard enough that this probably doesn't have to come down to money.
Of these schools, both Yale and Stanford have strong research emphasis. Many students at both take a year off for research - which could be great if you were interested in doing something more in-depth over-seas, or it could be something you're not into.
If I were you, I think Yale would be the next school that I'd drop. Columbia has a lot of diversity at NYP, and while Palo Alto is not diverse, Stanford students definitely rotate in hospitals with large Chicano, (and Vietnamese, etc) populations. Also, I'd much rather take the vibrancy of NYC or the pretty pretty weather of Palo Alto over the neither of New Haven.
I am less familiar with Yale, but both Columbia and Stanford seem to have quite collegial environments. Columbia is a bigger class - it seems like they have a lot going on within the medical school, but maybe a little less faculty interaction as a result of the class size compared to Stanford.
These are just some random thoughts...I don't think you can go wrong
At the end, putting all the logical weighing aside, is there anywhere where you felt like you "clicked" most?
but to each their own. I would probably pick from Yale or Columbia of those two (I want to stay on the east coast), and then probably pick Columbia (Yale's curriculum is too hippie-dippy for me). 
