I'd completely forgotten what the opening to FFXII was like, which is further evidence that I really need to replay the game. It's quite good, but it's rather drawn out, as VeloZer0 said.

I'd say FFVIII hands down. It's not one of my favourite entries in the series by a long way, but it's definitely got my favourite opening. Liberi Fatali is an excellent piece of music, the opening is exciting and edgy and gives some tantalising hints of what's to come. It's probably one of the few openings that has made me genuinely excited about what is to come.

There's a certain nostalgia value attached to FFVII's opening, which I felt this evening when I started a new game and played for about an hour or so, and I love the rendition of Terra's theme at the start of FFVI, and so they deserve honourable mentions. FFX's opening FMVs are also still visually very impressive.