I have lived in Houston most of my 52 years, and love it!
The pros:
1. It's so diverse - every nationality and culture is represented here - you can go to a different festival just about every weekend. This city just plain feels exciting. I work downtown, which is really booming now, and has a growing nightlife, including opera, ballet, theater, etc.
2. Employment opportunities are great right now. The medical center, especially, seems to be booming.
3. Three great seasons - spring, fall, and winter are wonderful.
The cons:
1. If you can't take the heat, don't even think about it - summers are brutal - it's the humidity.
2. Houston has finally clicked to the fact that roads are not adequate for the amount of traffic flow, and it seems like the whole city is under construction - it will be pretty bad for about the next 5 years.
I lived in Austin during my college years, and loved it - the hill country is incredibly beautiful, and, although summers are hot, they are not nearly as humid as Houston. Traffic is pretty bad, though, and jobs not as easy to find - every University of Texas alum would love to live there. I have only been to San Antonio a few times, but it's pretty.