I agree with everything EmailKid said above ^

The question for Must...Fly!, what do you want to do?
* Do you prefer cities or being out in the country?
* Are you into restaurants, nightlife, music?
* Will you be hiring/renting a car?
* What kind of a budget per day are you looking at?

While central Austin can be insanely busy, you can go out to the Highland Lakes and enjoy some time at a winery, some great restaurants overlooking lakes, and still enjoy some good music. If you really want to visit Austin, you could always stay out a bit and drive/train into town.

I've been to Houston many times and have a sister who lives in the area. If you want a city, it meets that. Sure there are great restaurants, museums, possibly some sporting events going on. But it definitely isn't New York City or Chicago...

Depending on weather, you might want to also consider some time near the beach/gulf.

That said, I like the idea of going to Big Bend. It is out there...not really easy to fly to, and you'll need a car. I've never been, but have heard it is worth the effort to get there.