Beavis and Butthead are two different guys, with no parents.
King of the Hill is a family.
NOTHING about those two shows is close, except that MAYBE they were both considered "bad" back in the day - but even then, Beavis and Butthead was far worse in that respect than Simpsons and that isn't even a comparison.
Peter Griffin = Stan Smith, both dads, both morons
Lois Griffin = Francine Smith, both moms, both annoying
Chris Griffin = Steve Smith, both sons, neither like their dad
Meg Griffin = Hayley Smith, both daughters, same shit
Brian/Stewey = the alien
They're created by the same people, written by the same people, clearly draw by the same people and use the same idiotic ZOMG LOOK SOMETHING happened humor - neither is funny, they're nearly identical except somehow American Dad is actually less funny than family guy (probably due to the lack of Stewey, who, every once and a while actually does something funny).
What about Beavis and Butthead (or Simpsons for that matter) is anywhere near close to King of the Hill? Not a god damn thing.