Years ago I flew Delta almost exclusively. This was when I was living in GA, near Delta's Atlanta hub. Service was decent, price not too bad, and fairly comfortable planes (or maybe I just got used to them and they seemed comfortable), but from comments on here Delta's gone downhill in terms of service. I'd probably still fly them, mainly because I have so many FF miles with them still.
US Airways is a main player here in Richmond, and DW Lauri and I have flown them a couple of times. Price about comparable to Delta, but DW and I haven't had a decent flight with them yet.
DW Lauri recently flew on JetBlue and had a great flight. Comfortable planes and great service, she said she'd definitely recommend them.