Fair question. It seems that compensation is determined largely by what Medicare/insurance companies are willing to pay for procedures etc. I believe unfilled fellowship spots aren't really a problem in any field, but the highest-paying subspecialties attract the most applicants. For example, cardiologists are very well-compensated, and cardiology fellowships are among the most competitive.
Right now I'd be leaning towards UF if I were you, I think, since my intuition is that $30-60K isn't much debt relative to what physicians typically make. But have you thought about using instacalc.com or some other spreadsheet to actually tally up all the numbers related to fees, cost of living, expected career earnings, time value of money/disconting, etc.?
Congratulations on getting admitted to medical school, btw.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.