I like the answer I created for my own forum a while ago. So I think I'll copy it to here!
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Good question. I have enjoyed all the FFs I've played but mostly for different reasons, so bear with me...
I started playing with 8, played X, X-2 and 12. With the exception of X-2, I've finished them all at least a couple of times. All of them have good and bad things, so I'll run down the list:
FF8 has a good story and strong characterisation, even if the characters are stock types and the plot has more holes than a Swiss cheese. It has the absolute worst system (drawing is a nightmare) but also far and away the best cut scenes, especially the ballroom scene which is an absolute masterpiece and arguably the high point of all the FF cut scenes. Watch the body language throughout and you'll see what I mean. Hero is annoyingly whiney, but that's par for the course with FF. You have a fair amount of freedom to move around, even quite early on, which is good. I like the card game, probably because I'm very good at it. If they'd dump 'Random', that is... Has the best use of limit breaks, with nearly every character being both unique and lethal to the Nth power. Has the most annoying main character, but some of the best supporting cast in Quistis and Rinoa. Ultimate weapons are challenging to get, but not impossible.
FFX has a good story, good cutscenes and solid characters - even if there's one too many and the story and system suffer because of it. The system is designed for six characters really and doesn't really work for seven, which is a design flaw. Has the best summons and the best use of summons. Also has the most annoying character in the form of Yuna, who keeps gratuitously apologising for nothing all the time and whose plans reveal her to have no sense or intelligence whatsoever. Half the time I want to yell at her for being so darned stupid, but it would be kinda like kicking a kitten and you KNOW she'd just apologise, which is even more annoying. X is well plotted for the most part, but FAR too set on railway tracks for the majority of the game. I loved Blitzball. It may not make any actual sense, but it's still the best mini-game in any FF I've seen thus far. Limit breaks vary in usefulness. Characterisation is solid if unspectacular. Best main character, but that's kinda damning with faint praise. Ultimate weapons are anything from hard to outright impossible.
FFX-2 has the great advantage of immediately giving you the whole world to play with and then NEVER throwing you on railway tracks. It also makes Yuna into an interesting character, which is a huge bonus. The characters shift between ability sets as you wish, but there are far too many ability sets ('Dresspheres') and training them all up would test the patience of a saint (So I certainly never got them all to full power!). It plays out like someone wanted to make a sequel to X without actually thinking about what made X so good in the first place. Worst combat system, though bound to appeal to people who like watching cartoon girls change between skimpy outfits (So that's about three people worldwide, then! ). Loved the coin mini-game because it really was very challenging, especially some of the higher rated boards. There were a few I never even tried and for people who can't do sums very fast in their head it would be nothing but endless frustration. I'm only quite fast, hence the few I never tried! No summons or limit breaks in the game. The plot is barely there and because of that actually makes more sense than any other FF game. Main character is solid if unspectacular. Has no ultimate weapons. Has a HUGE disadvantage in that it has multiple endings and there is no way of getting the good ones without a walkthrough.
FF12 has by far the best system - and I really mean by FAR! Not just the licence board, but also the gambit system that allows for real time combat where your characters can be programmed to act intelligently and you can actually see enemies on screen before you run into them. It also gives you a lot of leeway in where you can wander right from the start, so if you fancy forgetting about the plot and wandering around doing stuff for a few hours at any point, you can do so without being railroaded at almost any stage of the game. The downside is the plot, which makes no sense whatsoever, and the story much of which is blatantly ripped from Star Wars. They could have at least TRIED not to be so obvious. The worst thing about the game, though, is that the main character has no reason to BE the main character. Every other character (OK, bar Penelo) has a more interesting character, stronger motivations and a compelling back story that could have been used to drive a truly great game. It's like they picked the weakest character and made him the leader because he had nothing else to contribute, which is just painful. Summons are worthless and I'm not impressed by the limit breaks either, but the good news is that neither are needed. Has no ultimate weapons.
So - all have good and bad things about them. Plot holes abound, story often makes no sense - but all in all they are mostly extremely good fun to play as long as you don't pay any real attention to whether or not they actually make sense. Which means, for me, it all comes down to how good the system is... Which lands it firmly on FF12. For all my criticisms, I love the magic system, the combat system and the amount of freedom you get to just wander around and do what you like. Six characters are about right for the game, and you're not in any danger of levelling up to maximum before the end unless you are really, really determined to do so.
