Austin has the cool factor, but The Woodlands is not far from George Bush International and trust me I’d rather be in and out of travel as quickly as possible. I don’t know if it’s changed but one more advantage to Continental is they used to have a great first class upgrade policy, going by space available and not having to use mileage. As a single guy, The Woodlands might be a bit boring for you, I don’t know.
Again Dallas probably the most convenient for Travel followed closely by Houston. However Continental has hubs in Cleveland and Newark which cover the Midwest and East Coast more completely so you have a slightly greater chance of connecting flights in Houston.
With Denver, many of United’s west coast flights stop over there. However I don’t know if the reverse is true, that you can live in Denver and get to any city in 3-4 hours. Salt Lake city is a Delta Hub.
To that point I suppose Atlanta is possible. However the advantage DFW has is that American really blasts to about anywhere from Dallas.