Sphere grid, meh, my least favorite system of the three. Those just give the ILLUSION of character customization.
There's classic RPG style, as seen in 1, 2, 4, 6, and 9 (And breath of fire. and dragon warrior. and…) where characters leveled up and learned spells and increased stats at certain levels, simple as that. If they were a thief or a dragoon, they would remain as such the whole game and learn their best stuff around level 50 with the possibility of equipment changing what skills they learned. (I particularly liked 9's system, despite missable weapons)
There's all out job class system, where the job classes are the entire point of the gameplay and the story takes a backseat, as seen in 3, 5, X-2 and Tactics, they had complicated job class system where the entire point was to learn a lot of abilities, change to a new job and learn more abilities, and in the end, main 1 job while mixing in little chunks of others. Great system, but it destroys character uniqueness.
Then there's… what 7, 8, Crisis Core and Dissidia did which kind of mixes the two. Where the characters had abilities unique to them and would learn new unique tricks along the way, but junctioning could change around their entire secondary ability set so you could end up with completley different characters, or completley similar ones. Scarcity of certain materia and junction monsters kept it from happening too much. (Everyone could learn Fire and Cure, and you could eventually have multiple copies of Knights of the Round, but why would you want to?) Obviously Crisis Core only has the one character, but he's pretty damn customizable. Ultimatley it still downplays character uniqueness, but... (And Dissidia being a fighting game they're all quite distinct)
And then theres sphere grids, as seen in 10 and 12, which as I said, just have the illusion. I don't like them… Sure, you can have a character just sit at the start and then teleport them around later on when you have the ability to do so, but then they miss out on everything along the way. In 10, a character is going to go down their pre-set path for 90% of the game (excep Kimahri who gets stuck as a whatever) and in 12, everyone has the exact same grid and starts in nearly the exact same place. Apparently the international version added job classes, but then your stuck in one the whole game, and theres only 6 characters and 12 job classes, which is the exact opposite problem. So in 10 the system is adjustable near the end, but otherwise its just pretending to give options, its basically just an old school rpg where you get things at a certain level, and in 12 all the characters are IDENTICAL except for the visual on their limit breaks. Bleh.
And 13 is following that path? Well, hopefully they've figured out the quirks by now.
I rather liked 9, which adhered to the old school. Ever character had their job class so you picked out favorites that way, (though Steiner doubled as a balck mage if orco Vivi was in the group)but for 4/5 of the game the story would mix and match your party forcing you to use everyone. Along the way you could, and pretty naturally, ended up mastering most of the secondary abilities, but never had enough points to turn them all on, so you always had to pick and choose. And sometimes you'd get three new items at once with different abilities, but could only learn one at a time, so you picked and chose.