IX.
There is no other correct answer. Get IX.
Do it for this little guy:
In my opinion, Final Fantasy IX is not just one of the best Final Fantasy's, it's one of the best RPG's in general. Between the amazing cast of characters, the gripping storyline, the amazing soundtrack, the fun combat system, Final Fantasy IX is a masterpiece.
Unlike VII and VIII, the game goes back to the more medieval-esque setting of the older Final Fantasy's. It's essentially an homage to past Final Fantasy's.
The combat system, again, unlike VII and from what I can tell VIII, makes each one of your party members unique and have a use, as they each are essentially locked to their specific job class rather than the past systems which make every character essentially blank slates that can do anything. (Not that that's a bad thing mind you, I just happen to prefer the system used in this game.)
The story I feel has just the right mix of seriousness and lightheartedness. It tackles a couple of serious themes, while at the same time, it doesn't really feel overbearing. It that makes any sense.
The characters are all likable and well developed for the most part. Some more than others admittedly, but I still found myself attached to them. I wanted them to succeed, I wanted them to be happy.
By the time it was over, I felt an immense sense of satisfaction not very many games give me. To me it was an amazing experience.
I might be overhyping it for you and I know I sound like a fanboy, but that's just how I feel about the game. It holds a special place in my heart, as cheesy as it sounds.