Having flown Southwest Air, Delta, and American within the last few months, I have to give the nod to American. A little more leg room in the regular coach. And I think the staff is a little more friendly.
Circumstances dictated that I arrive 5 hours before my flight from Pittsburgh to West Palm Beach with a layover in Charlotte. The part of the airport was empty and I was chatting with the cleaning crew when an agent arrived at the gate. He asked why I was there so early and then, without asking, found me a seat on a flight to Charlotte that was currently boarding. I know that I still had to wait at the layover instead of Pittsburgh, but this gave me time to get lunch there instead of hurrying from one gate to the next.