Southwest is cheap and fun.
Kids get to go in first =).
You get to chose your seats.
Free beverages.
Very comfy seats ('cept on the -200s, where they are slightly ripped from 20 years of service xD).
Also, now, Dallas Love field can go to states beyond the bordering ones from Texas, which opened up a lot of new routes, it also saves you an hour from going to Hobby then to wherever.
I like southwest, but I have only been on another airline twice, and that was when I was alone (American Airlines on a MD-80, I went to fly to my mom from Austin to Oakland for her Ebay Conference, the flight made my ears pop A TON of times, didn't like it at all).
Also, I did like continental, but they did nothing to accommodate my brother, who is special needs, and the seats are assigned.