I have to go with KH2. I remember being absolutely blown away at how much better (graphically) it looked then the KH1 opening. It managed to cram the story up until that point within the duration of the new theme song. Every opening since has essentially done that (although I haven't seen 3D's opening so I can't speak for that) so it's kind of lost it's amazement, for me at least. Still, they always look amazing. You can always count on Square to give you amazing visuals, if nothing else.