Firstly, congratulations on your admission to multiple medical schools. You're in the best of difficult predicaments.
Secondly, matching to a competitive residency is heavily dependent on your USMLE scores. Do note, however, that matching to a competitive residency at a competitive LOCATION is highly correlated with where you went to school. If you wish to do your residency in Texas, then UT Houston is the no brainer. If New York is your thing then by all means go to Columbia. To each their own.
Thirdly, I would look at US News or MSAR for average graduate debt between the two schools. According to US News, UT Houston's average is around $110k whereas Columbia's is around $130k. Interpret these averages as you will, however, also take into account the variables influencing student debt (financial aid, scholarships, parental contribution, etc.)
Of course, after looking at the logistics of each school, you need to ask yourself "If financial obligations did not exist, and matching to a competitive residency location was not effected by the school I attend, where would I be the happiest?"
Debt can be paid off, and matching to a competitive residency is very possible with either of these schools, but time is something you can never recover. Furthermore, only YOU know where you'd wish to spend time learning the art of medicine.