First of all, i don't see this topic as being fair at all
Simpsons has declined, it's undeniable. It's been around too long to still be in it's hayday, not to mention it lost several writers to futurama when that was around (i'm pretty sure they cancelled it).
Family is still relatively new. And just has a different approach to things. Personally, OLD Simpsons vs. Family Guy, it goes to the Simpsons. But i refuse to vote because the question is not about Old Simpsons vs. Family Guy.