Futurama would definitely be the best out of the lot. Never panders, always a little hint of self-deprecation, but always classy (in their own unique way). And if not classy at least funny. Apparently funny is an important element in comedy shows.
I like to imagine that they use it to purge out whatever unpleasantries that stems from the mainstream pandering that the Simpsons thrive on.
If we're talking Adult Swim in general though I've always loved Space Ghost Coast to Coast and Harvey Birdman.
Oh wait I've completely contradicted my previous stance with these statements. Whoops.
Here's a question, and something I've yet to still grasp - what exactly is so enticing about the Flat-4s? People around here rave about them in general, so I guess it's something you'd have to hear to understand. But I'm still curious as to why exactly they seem to command the praise that they do.