XII is my first choice as it's depth and scope is greater than most of the series. I never liked X and actually found it to be pretty boring, in fact (to me at least) it's the most boring storywise of the three you mentioned. X-2 is a game you play for gameplay and little of anything else...

Seriously though, play FFIII DS cause it's got sexy graphics and is good overall. I also feel you should give the earlier games a shot cause I can't necessarily say the recent generation is the best.