IMO, Houston is only worth it if you go with a local. There are great restaurants and bars, some world-class museums, but it's a tough city to get to know as a visitor.

San Antonio is great. I've lived in both cities.

If you can swing it, stay at the Hotel Emma in San Antonio's Pearl district away from the downtown Riverwalk. In fact, just never go to the Riverwalk.

Dine at Pearl's restaurants, get some cheap tacos out in the Deco District or Southside, rent a bike and see the historic Missions trail. Hit up the trio of Hot Joy, Chisme and Barbaro (three restaurants from the same guy). Chisme's Tuesday happy hour on the patio will keep you happy for hours. Bar-crawl in Southtown.