Family Guy is best, because it's so completely unpredictable, retarded, and messed up. Just the way I like it. The Simpsons are funny while their stories are still being believable, while Family Guy just ignores realism, and common sense, altogether.
Oh, and Mayor West is my favorite character in Family Guy...
Like when West gets hit in the face by a brick, and his nose starts bleeding, and he yells, "My God, I'm a tomato!"...
The Simpsons all the way. Family guy doesn't suit me at all. I like Homer and his d'oh! Bart is a nice element to the show and so is Lisa. Marge is just funny by being so uptight and it's funny how Maggie is the smartest one at times.
Three years ago, I would have picked Family Guy. Now I think they go too far with their jokes, so I will pick the Simpsons, because they are still pretty funny to me.