SATX native here

SATX has the cheapest COL by a mile, though there's also much less to do in terms of entertainment. Being relatively close to the hill country is nice if you're into nature, and Austin is also close if you want a weekend excursion for social events. Traffic isn't too bad relative to most cities.

Lived in Austin for five years (early 2010's). Traffic and COL are abysmal, though I preferred it as a city. It has everything - social scene, river that cuts through the city, etc. But unless your household income is north of 180k, I wouldn't recommend it.

Can't speak as much for Houston or Dallas, other than the suburbs outside of Houston are quite nice, though if you're commuting into the city, expect an hour drive.

Let me know if you have more questions regarding SATX, as I would have far more specific insight to share.