It sounds like you want UTSA more than UTMB. In terms of tiers, they're much pretty equivalent in the middle. It's likely you won't have significant difference in your career going one over the other. Frankly, if you really think you're happier in SA, then you should go there.
However, for the record, some information is inaccurate:
"UTHSCSA is directly connected to a major medical center, and although UTMB rotations go through TMC it's still an hour drive on a good day"
If you choose to go to Houston for rotations, you won't be driving from Galveston, and it'll likely be <15 minutes away if you rent close. If you choose Galveston, you'll be in Galveston.
"UTMB has a higher STEP1 average than UTHSCSA, although this could be attributed to them having the highest matriculant GPA in the country (3.91 vs 3.73)"
It's mostly the change in curriculum towards boards focused classes that is attributed to the 241 average Step 1 Score for class of 2019. UTMB used to have similar GPA matriculants but significantly lower step scores.
"UTHSCSA has a little less NIH funding than UTMB ($66.8 vs $67.2 million)"
UTMB has significantly higher NIH awards in 2016: $73 million vs $53 million
"UTMB has a lower average graduate indebtedness than UTHSCSA (~$130k vs ~$97k)"
UTMB average graduate indebtedness is 80k.
"UTHSCSA is ranked higher in both primary care and research than UTMB (according to USNews)"
UTMB is unranked because it did not submit a survey to US News. It's not a fair comparison. According to StartClass (
http://medical-schools.startclass.com/), UTMB is ranked 50, while UTSA is ranked 58, based solely on comparable data on medical schools from official third party sources, including admissions data, GPA/MCAT, and NIH funding.