Trey Parker and Matt Stone, the creators, writers, and pretty much everything else of South Park, recently gave an interview to the Montreal Mirror. One of the topics they touched on was the rivalry with Family Guy:
M: How do you feel about Seth MacFarlane’s empire?
TP: There’s more and more stuff every day finding its way onto American television that I think is really great, but then you get this bubblegum shit that’s just, like, by the book, what we call 9-to-5 comedy writers. They mostly have families and kids and that’s the most important thing and then they go in to work and write comedy and when it’s five o’clock, it’s time to go. It’s gag humour, and gag humour drives us crazy. Where it’s just, like, “Here’s a gag, here’s a gag”—it’s got nothing to do with what’s going on in the show, just like, “Here’s a gag.” And anyone who writes comedy knows that that is the very easiest, simplest thing to do and you don’t really need any talent to do it, you just learn the craft and do it.
MS: Yeah, Family Guy’s just not a show I like. It’s funny, when we did that [Family Guy parody] show, it was more to point out that the similarities between our two shows is that they’re animated, and it stops there. They feel like very different shows. Family Guy, to comedy people, it’s kind of what that band the Offspring is to real punk rockers.
TP: The biggest thing is that you essentially kill yourself for a show—it’s like, you’ve got to die for it. When you’re an artist, you’ve got to say to yourself, “This is all that matters, and if it kills me, so be it.” And then you have the Family Guy writing staff who come in 9-to-5, write their gags and go home. But what I absolutely must say to you is that this totally, purely 100 per cent completely, comes from a place of jealousy. Because when we’re sitting there in our room, it’s three in the morning and we’re 12 hours from having to air and we don’t have, like, a third act, wondering why we do this to ourselves, we’re just totally jealous of their job. Seth MacFarlane is basically in the same position as us except he hasn’t written a fucking thing in four years. I wish I was him. – source
Honestly, I think there’s plenty of room for both shows to succeed; it just makes them look silly when they try to do rivalries like this.