I have ridden both, and I think IASW by a country mile. I would ride both again, definitely. But I remember riding Na'vi shortly after Pandora opened and kind of feeling like "that's it?" afterward. Especially, as others have mentioned, given the wait times that were involved at the time. I mean, it was fine and it certainly is pretty. But it's short and there's no story to speak of and it just feels... underwhelming. Not bad. Just not great.