VII's was the best executed, it just threw you in and set the mood straight away. It might just be because it was my first FF, but it also made it more surprising every time you realised how huge the game and plot was getting. The intro just showed Midgar, so when I finally got to the world map I was like "What the Hell? There's more!!!"

VIII's is the most entertaining to watch though, so as a stand alone scene it gets my vote.