I also think Avatar was a better film. And I would add a 'much' in there to boot.
But while Avatar had a better hold weekend to weekend, it would have been almost impossible for Avengers to retain that hold after a 200 mil opening (Avatar's opening was a fraction of that). I think the third weekend will tell whether or not Avengers has a chance of surpassing Avatar's domestic take (or Titanic's, for that matter). This is an event film with audience response so positive it's almost ridiculous. It's possible, but it's going to depend on the third weekend drop. If it lowers another 50% or more this isn't going to happen, but there's no telling at this point.