Back in the good old days (pre-RJs), this question was a no-brainer - DL at DFW. Lots of flights, lots of destinations, and all in one terminal (anyone remember the "Easy Street" ad campaign?). They even had real international service (to Europe) once upon a time.

Of course, with all of the RJs and other service cutbacks, those days are now gone forever...which is why I now fly AA. Granted, I'd hate to have to connect here with AA now being spread out over three (and after 2005, four) terminals.