I played X-2....own it beat it.....preferred 5 still

FFVI

 The job system in X-2 is possibly the worst ever imo. They had a nice list of jobs, but the mechanics behind them sucked hard. There was no benefit to mastering a class, and no real way to bring over some of the essential skills to other classes. In the end it was best just to choose a combination of three classes you liked and stick with it throughout. FFV/Tactics job system was in every way superior. FFV just needs to have 2 accessories ala VI.

You could swap jobs right in the middle of battle anytime you wanted too

And its a little unfair for you to judge X-2 for not having lasting benefits for the job classes when I dont remember none of the other FFs with JC having lasting effects either.

Certain Jobs are more useful in different situations against different enemies. I would find myself swapping alot through secret dungeons etc.

and in case you didnt know........

X-2 also had items/equipment that would allow you to access other job class's abilities without changing. Thats not even counting the fact that the ultimate gamerments(Jobs) in FFX-2 were combinations of all the jobs combined, including their own seperate party members(sort of).

EDIT:

And you gotta admit. The Beserker, Samarai, Dark Knight, Beast Master and Gunner were some badass job classes.

XII for me, I liked everything except the license system, it could stand to be refined a little. The FFVII materia was genius as well, love how you upgrade them and spawn new ones!

FFXII. I liked 1, 2, 3, 6, but i hate their systems. I also hate having 4000hp and doing 3000dmg to enemies with 15000 hp, but thats in all FF games minus tactics so....
(I prefer Fire Emblem style: 15 attack - 8 defense = 7 dmg). I also liked the gambit system and the method for learning to equip items, etc, in XII

I like FF3's job system, if the monster visablilty of FF12 was mixed in with FF10's combat system then it'd be really nice

FINAL FANTASY 9

If we're talking about the main FF games (and not XI either), I would have to go with XII.

XII had some serious flaws, but with a few fixes it could be really good.

Gambit System -- If they had just given us access to all or most of the gambits from the get go, it would be quite good.  By the time I actually started getting interesting gambits, I stopped caring about the system.

License Grid -- It would be good if every character didn't have the same grid. Since it has the same grid, every character ends up being exactly the same.

FFX for me