Slow outdoor hardcourts. That being said AO is my favorite slam.
AO is my favourite slam in terms of atmosphere but they severely degraded the quality of play with that swamp of a surface.
Clay. Rewards running and retrieving to much. Clay is the surface that allows the less talented players an opportunity to flourish. Just play great defense and you've got a chance on this stuff.
At least it's always been that way. When they turn a surface which has to help offensive players into a pushers' paradise, you know it's wrong.