Unfortunately there's not a true to mesh all those elements together, mostly because the settings can vary from medieval to futuristic. I find the one that would be the simplest to make into a movie would be the first one, mostly because all of the other ones have such an in depth and intensive story line the movie would either have to have multiple parts, or be reeeeally long.
I think the game that would make the best movie would be FFII. The story itself seems like a movie with all the betrayal and war and death.
However; what I truly want to see is the opera from VI as an actual opera. I've seen performed at the Distant Worlds concert, but I'd love to see it more detailed and fleshed out. That'd be awesome ~.~