Was all excited for the Final Fantasy sale then quickly realized it's not live yet. Which the heck dissidia do we want? And I am guessing all the PS1 games are straight ports, crappy graphics and all?
Duodecim contains the original Dissidia's campaign as an unlockable after you finish the game, so get that one. PSOne versions are ports with some minor updates, but I don't remember what they all are. I think each has an opening and ending movie that was added, and some include updated translations. (assuming you meant 1-6, 7-9 are the same as ever)