I haven't flown Delta often in recent years, mainly American for where I go. Never any real problems with Delta when I did fly them. Only time I remember getting stuck in Atlanta was due to weather, nothing Delta could control. I think I read they have (or soon will have) a direct flight to Austin so maybe will be flying them in the near future. American's been pretty good, just a few problems for me. I think they went downhill a bit when they merged with / bought out USAir. The NY airports (and many of the older US airports), in general are dumps compared to much of the US, and especially much of the rest of the world.
For those that don't enjoy the seating arrangements on Southwest, you should have been around when People's Express existed. I lived in Philly back then and flew them out of Newark a few times. It was like boarding a bus. You board, grab a seat, and then pay for your seat in cash on the flight.
Was a cheap flight back then, but it was nuts. Back then, they were the only (and 1st I think) airline to charge for checked bags.