This is my favorite animated show of all time. It's humor, while raunchy, is very realistic and nostalgic, and there is some very clever dialogue. It does have some language, drinking, and smoking, but there are positive messages on occasion, like about growing up and being responsible parents.
Unfortunately, I am still not old enough to see Family Guy, and I'll bet that will become my favorite animated show once I start watching it.
But as of right now, King of the Hill is definitely my favorite. It may be mature and hard to understand for young kids, but those old enough to "get" it will have a great time. Five stars!