In the MU I'd say the Avengers and FF are more respected by the public and not feared as the X-Men.
But when it comes to sales I don't think even when John Byrne wrote the FF in the 80's were sales ever high, ditto for whichever creative team was on Avengers. The X-Men when it came to sales buried them both.
Maybe Avengers was selling well with the whole Secret Invasion, Civil War but not like X-Men numbers.