I'm a teen guy who started watching this in 2009. Out of both series, I can safely say that the early episodes of each series were better as a whole since they didn't have as much drama as the later ones (esp. relationship drama, which often makes me want to hurl). By the same token, episodes involving large amounts of relationship drama (*cough cough* "The Play's the Thing") were the worst ones in my opinion. Comedy is better than drama in my taste.
Aside from this, my favorite shows include American Dad!, China, IL, Family Guy, South Park, and The Simpsons.