I know they're not exactly positive role models or anything, but I think what endears them to me is that they have about a hundred times more depth than the cast of "Family Guy". Episodes like "Roger 'N Me" and "The One That Got Away" have an emotional core that you'd never find on "Family Guy" these days, and it makes the characters feel a lot more real. Yes, Stan's a shortsighted blowhard, but he does what he does out of love for his family, even if his way of showing it is extraordinarily inappropriate. Yes, Roger's a self-centered drunk, but he's still got feelings, even if he has a hard time expressing them. Yes, Francine can be whiny, but again, she's always got her family's best interest in mind. Steve may be kind of a jerk sometimes, but it's because he's got such an unwavering faith in his dad, and you just realize that he's a good kid who picked the wrong role model. Hayley may be aggressive, but at least she stands up for what she believes in, and that's extremely admirable. And sure, Klaus is a pervert, but who cares 'cause he's in the body of a fish and he can't actually act on his urges.
These little touches ground the characters in reality, something that "Family Guy" doesn't bother with. And I prefer a show with a structure behind its madness rather than a show where the only rule is that there are no rules. Anarchy sounds like fun at first until you realize that the law of the land existed for a reason.