I'm bored and I can't sleep. And because of this I have decided to rank the Final Fantasy series from worst to best.
A quick note (though it really should go without saying): this is based entirely on my opinion, and probably says more about me than it does about Final Fantasy.
Now then, here we go, starting from the bottom:
IV. How so many people rank this so highly I will never be able to understand. For a game that calls itself an RPG, Final Fantasy IV really doesn't let you do much. You can equip your characters with weapons and armor, walk from town to town, and press A repeatedly in battle until all the monsters are dead. Aside from that, the game tells you who will be in your party, when it will change, when your characters will learn new spells (and which spells they will learn), how their stats will increase, pretty much all the fun stuff that this type of game is supposed to let you play around with.
I. Seriously outdated. It may have been considered a good game twenty years ago, but it's 2010 now and a lot of things have changed. Random encounters up to your ears in this one (at one point I took a wrong turn in a cave and ended up fighting monsters literally every step of the way). And you have to grind to get enough money to buy anything useful. But hey, at least the game lets you pick your own party, unlike a certain other game I have previously mentioned.
II. Interesting stat growth system, which I think may have been a bit ahead of its time. Other than that, it's in the same boat as the first: time has not been kind to this game. Grinding isn't as fun as it used to be back in the day. And I'm not entirely convinced that grinding was ever fun to begin with, anyway.
III. More jobs than FFI means more freedom and a more enjoyable experience overall. But still suffers from the ravages of age. DS remake can't hide this fact behind updated 3-D graphics, no matter how adorable they made the characters look.
VI. A lot of people seem to worship this one for some reason. I don't get it. Lots of characters (almost too many if you ask me), but they're all fixed into jobs you can't change (ranging from completely useless to way too powerful). Once you get espers, you get to turn them all into mages and apply minimal pointless stat boosts to them. Oh goody. There are a couple of neat things you can do with relics, but that's about it.
IX. A more modern Final Fantasy that feels like an old-school Final Fantasy. Which comes with its own set of problems. Like eight characters with fixed jobs. Which I don't like. But at least you get to decide (via your equipment choices) in which order they will learn their skills/spells, and you can customize other abilities (such as immunity to poison or auto-regen) as well. And the characters feel very well balanced; you can basically pick any combination of four and have a workable party. Probably the only fixed-job-type game in the series that I can actually have some fun with.
V. Among the older Final Fantasy games, this is the only one that holds up relatively well today, thanks to its innovative mix-and-match job system. When your white mage isn't healing the party, why not have her crush monsters with her bare hands? Or make a thief who can use magic to bend time and space? Or turn someone into a dual-wielding rapid-fire spellblade monstrosity and create some real carnage?
VII. One word: Materia. The first game since Final Fantasy II to give you real freedom in building your characters your way, without the restrictions of FFV's job system (there aren't many, but they're there). The graphics didn't age very well (Lego Final Fantasy, anyone?) but that doesn't really hurt the rest of the game much.
VIII. Even more generous than FFVII in terms of character customization, this is arguably the single most customizable collection of characters in the series. Using the junction system, you can individually adjust every stat for each character, and decide exactly what kinds of skills and abilities you want them to have. Also, the card minigame by itself is actually more fun than Final Fantasy IV in its entirety. People complain that it's too easy to make broken characters, but to me that's more a matter of self-control than a problem with the game itself. If you destroy the game's difficulty/fun with your super junctions, you only have yourself to blame.
X. This is the first time I'm going to mention story, because IMO this is the first time in the list that a Final Fantasy has had a story worth mentioning. The fact that the characters have voices and facial expressions and body language just make the whole experience that much more engaging. The sphere grid starts out a little restrictive, but that goes away fast, opening up customization greatly. Also, the new battle system finally gets away from that tired old ATB gauge, letting you plan out your battles several moves in advance (which can save your life in a couple of the really tough boss fights). Some people complain that the game is too linear. To these people I say all FF games are linear; this one just does a worse job of hiding it than the rest.
XII. No more random encounters. That alone is reason enough to put this game on top. Add to that a refreshingly different story (there's that word again), a truly interesting world brought to life by all the interesting little tidbits of information you pick up on your travels (read the bestiary if you don't believe me), a gambit system that takes the tediousness out of grinding without taking the fun out of battles in general, monster hunting for that extra bit of challenge, and a fair amount of character customization via gambits and the license grid, and you've got yourself one fine game.
And that's all. I can't rank Final Fantasy XI because I haven't played it. Ditto for Final Fantasy XIII. I suppose if I wanted to, I could include X-2 somewhere (probably right before FFX), but since it technically isn't part of the main series I left it out. Anyway, if you took the time to read all this, you are a more patient person than I am. If not, then this is for you:
tl;dr version: (worst) IV < I < II < III < VI < IX < V < VII < VIII < X < XII (best); XI and XIII = no comment
Feel free to agree with everything I just said. Or, if you really think you must, go ahead and tell me why I'm wrong/crazy/a terrible person for liking a game you hate/hating a game you like/crushing you beneath a towering wall of text. Heck, even let me know if you think that Final Fantasy is bad and that I should feel bad for liking it. Or don't. It's up to you.