I'm not under the impression that UTSA is on the same level reputation-wise as UTMB or UTH, but feel free to flame if that's not a widespread opinion.
As for UTMB vs. UTH, here's how I see it:
UTMB >> UTH in preclinical -- better curriculum, more relaxed, much, much better step 1 scores
UTH >> UTMB in clinical -- it is the TMC, after all. Plus, UTMB is really struggling to keep up their patient population (hence their continuing shift to med education in Austin, both students and residents). And UTH's match list is seems to be a step ahead of UTMB's.
Finally, Houston >> Galveston.
If I had to choose, I pretty sure I'd go with UTH, even with the major downside of the preclinical curriculum and the low board scores that seem to go with it.