My two cents:
KSFO is basically impossible to run using the realistic setup of departures on the 1s and arrivals on the 28s.
KLAS is pretty good. Only gripe is too many commercial arrivals on the 1s/19s. In multiplayer, it's one of the few airports where tower is more challenging than ground.
KPHX can be really fun during busy periods. Primarily an AAL and SWA hub, so traffic variety is not its strongpoint.
KMEM is the weakest of the bunch. Unless you have a FedEx fetish, there's not much here to excite you.
My ranking would be KLAS, KPHX, KSFO, KMEM.
For each of these airports, I'd definitely recommend using a custom schedule. A list can be found here: