I'd post my Southwest opinions, but Elissa pretty much covered them. No seat assignments and the condition of the planes do it in for me. And yeah, they're no bargain any more. I pretty much have no airline preference, as they all pretty much suck these days (customer service?!? HA!). The destination usually determines which one I'll take (going south = Airtran, for example).
I will say I like the reasonably priced business class upgrades on Airtran. And how you can earn free ones after some flights. That's pretty cool...
dt