I voted SWA!
We used to use USAirways and still have lots of FF miles with them but the last 2 times we used them, about 3-4 yrs ago, our luggage did not arrive with us. This is beyond annoying when leaving FL on a cruise!

It's not like they could just deliver it to our hotel later!
Since then we flown SWA about 8 RTs and love everything about them:
1. Very reasonable fares, if not downright cheap ($39 in Sept and were getting $49 later this month!)
2. Their schedule rarely changes. Though they don't allow you to book 11 mos. in advance, once they release their schedule, it's done and only weather has caused us delays. no bs excuses.
3. Never any change/cancellation fees. You can change your mind 6 times and not cost a dime.
4. If you find your price has dropped, you can rebook it and pocket the credit for which you have 1 yr from original booking date to use. This is so nice, we've actually saved enough credits to book another trip!
5. By the time you walk to baggage claim, bags are actually coming out!
Hey USAir, come take some notes!
6. Sounds corny but their employees are really nice and seem happy in their job. We've played Disney trivia at the gate once. They crack jokes during takeoff like, "whoever has a blue Honda, you left your lights on!"
It's not that funeral mood like USAirways.
7. People sometimes knock the 'no seating assignments' but we find it's fine. We have 2 young children and have always been able to sit together. Even when we had assigned seats on USAirways, every time they changed the flight time or # we'd lose our seats and I'd have to call to have them re-assigned. This would sometimes happen 2 or 3 times per flight. ugh!
8. They have plenty of non-stop flights from Philly. Why drive all the way to Newark? I've looked up Spirit many times but they can't seem to beat SW prices and I don't believe you can get a credit when the price drops but not sure on that.