The Simpsons is funny as hell, but American tv is also responsible for shows like "The Fresh Prince of Bel Air", "The Tom Green Show", and "Married With Children". My local tv station gets a plethora of American "comedies", and every time I hear the laugh track on those shows, I stop and say "Where was the joke there? Did I miss something?"
Truth be told, both sides of the pond produce untold of amounts of garbage masquerading as comedy. However, personally I think that Britain has a much better quality/shit ratio going on. And this is coming from an Irishman! We're supposed to hate the Brits!
Just a matter of taste I suppose.