If by service you are referring to people, then I'd have to say DL is at ir near the top.
If you want to talk about just FA's then DL is at or near the top.
Some phone call centers are more friendly and just better at what they do than others. But DL, as a rule, beats the rest here too.
NW has, IMHO, the best on-line support. Friendly, live-chat to answer questions. And the same person can answer your flight and WorldPerks account issues. No transfers needed ... nice. But the NW FA's are usually ... surley at best ... you get the whole can of Pepsi in coach on NW but get dirty looks if you ask for a pillow ... consistantly. Sorry, no offense intended to anyone, but that's been this customer's experience. AA's are mediocre at best.
And then there's SWA. They should be teaching what "service" is to everyone else. At the cattle call, I'm a happy steer as I'm prodded into my place. When's the last time an FA or GA for one of the majors actually tried to make the flight "fun". Yeah, it's a cattle car with no amenities. But the people really try to make you smile through good attitude.
There's good and bad everywhere. Pick your poison.
edited to add: Do we even want to talk about ASA??
[This message has been edited by theDeltaFlyer (edited 09-29-2002).]