I love dem both too.
I think that the whole 18 season argument isn't that impressive, because I think that some of the seasons were pretty half-assed. Overall, Simpsons is a historical show, A pioneer in comedy cartooning, and Family Guy only exhists due to the breakthroughs of THe Simpsons.
Family Guy is still relativly new, and definitly can prove itself to be just as spetacular. To say that Family Guy is relaying too heavily on pop culture is a bogus complaint. The show is based on relaying on pop culture. It is about a guy whose reality is warped by TV. If you watch the first Episodes, they originally wanted each episode to begin with a parody of something on TV, later, they just put pariodies everywhere. There will always be pop culture to make fun of, and Family Guy does have potential to last quite a long time. The thing that family guy did, was a entirely new angle of comedy, and you find that things like robot chicken are taking cue from family guy.