For me it was toss-up between The Simpsons and the Family Guy. The Simpsons has the longevity but jumped-the-shark after the Phil Hartman tragedy. Basically i asked myself if both shows were on at the same time and could only watch one, Family Guy wins for more laughs, more pop-culture references per episode.
King of the Hill is hit-and-miss, but the episode where Hank bought crack thinking it was fish bait was hilarious.
Theres people out there watching Futurama?