Family Guy for sure is my No.1.
But I'm also quite into the oldies/classics. I like The Smurfs, Tom&Jerry, Bugs Bunny, etc.
I'm quite a sucker for Eastern European cartoons before the end of communism. E.g. Balthazar or Lolek & Bolek.
The Simpsons are classic! It's the longest running cartoon and it has some credibility being in the movies and all. I love Bart and his antics. Every character is so funny.
A long time ago, I grew up watch AH! Real Monsters on Nickelodeon. I wasn't young at the time, maybe 17 back then, but I still loved the show. I enjoyed watching every episode, and I was sad when it never came on again.