I personally love American Dad over The Simpsons, that is a better comparison as Family Guy and The Simpsons run in different formats. American Dad and The Simpsons use situational humour while Family Guy uses cut away gags.
Yeah, those can be funny, but I prefer The Simpson's humor for the fact that it's always related to the situation. I dislike American Dad (the title isn't even correct...) because it's just Family Guy without the silly gags. What remains is a show trying to be funny.
Futurama is kind of... meh. It's mostly the same humor The Simpsons uses, but I still think The Simpsons is better, because it uses normal characters and situations, and not aliens and robots.
Though personally I think all of the above have gone downhill by alot and not as funny as they once where.
Earl had only just started. It's going down hill from now on, and soon it will be so terrible you will do everything for us as long as we stop! Our plan is succeeding!