Probably XII is the best example. The story is one of the few that could actually work for a movie. Most of the others may work for a film, but the films would be absolute crap.

XIII for instance would be a horribly cliched movie although the transition would be easy due to it's linear path. X could also be done in a movie but again, it'd be a pretty bad film.

Earlier FF games likely have too much to cover in the scope of a single film. FF VI & VII could work but would just have too much to cover and may suffer unless it was made to a LoTR length film. VIII I think is too convoluted whilst IX would have to be done as an animated film as part of the charm is the art style. 

The Crystal Bearers.  Srsly, rockabilly soundtrack and all.

FF XIII - all you need is cutting out gameplay part ;)

well said. that's why i picked XII for movies. Personally, i really want a TV-series based on VI. the character development of VI is so awesome. All the twists and hangs are too much to handle in a two-hour movie (you know you have to destroy the world once...).  On the other hand, while XIII is easy and linear to adapt to movie format, it lacks the drama, twists and storyline progression of XII. So Final Fantasy XII the Movie, i say.

Probably FFVII. Hence why they did make a movie.