I was born and raised quite close to Dallas! I've lived in both Dallas and Houston, so to answer your question, I'd say Dallas without a doubt. I'm not a big fan of either city, but I completely hated Houston. It may just be my large-city fears, but I found people in Houston to be a bit cold (apologies to any Houstonians reading, this definitely does not apply to everyone!), driving there was possibly the most terrifying experience of my life, and the summers are unbearable (for me, anyway). If it were me making the decision, I'd stay in Dallas *shrug*
And please, please don't be offended, Houston people. I may have just had a bad experience. I love you, really :\\\'(