I like Southwest a lot. Reasons I can think of:
NICE new planes.
Winglets on 73G's.
Consistent profit earning.
Laid-back boarding procedure. (cattle-call)
Easy booking online.
Drawbacks to Southwest are:
Not-so-nice older planes
Laid-back boarding procedure
I live in Dallas, so due to the Wright amendment, I never get to fly WN
unless I am elsewhere in the States.
I also admire AirTran, and anticipate flying that airline someday. AmWest does nothing for me. ATA is one I would like to try- I helped my friend book a ticket on them last October, and they said it was great.