Wasn't there a tier list thread that was essentially this very question?
...Actually there wasn't, that was just Mikey's thread on their playthrough of FFIX. God, I miss them.
Anyways, I'll just share what I said back then since it's still applicable.
The definitive FF tier list.
S-tier is honestly, close to broken. No bad match-ups. Represents the truly best the FF series has to offer. The most important thing in this series is "character." Character, character, and character. If you're in S-rank, that means not only do you have a solid combo game that you can pick up and enjoy, but your character building, style, soundtrack and art style match-ups.
Addendum, I'd probably put XIV Shadowbringers/Endwalker in S tier now.
A-tier is basically everything that's good but isn't uber broken. Which is honestly a lot, considering most franchises. These have mostly great match-ups for everything but the S-tier which kinda sucks but a skilled audience can really get around the S-tier character's unique character cross-ups and actually pull a win with their own strong mix-ups and mostly safe combos. FFX
and FFXIV are sorta anti-meta in that sense given they actually go hard against S-tier in the hands of a really skilled and dedicated player. This is no longer true,
XIV is meta 100%, be prepared. The strong and sudden win Emet-Selch pulled off last year at NHK put FFXIV in the meta and I don't see XIV going anywhere but up. Same for X. People shit on X-2 but they don't know what they're talking about or just hate lesbian fighters.
B-tier is good, but if you're in this tier, that means you have a significant number of really unsafe moves in your game that can destroy you in a match-up or just keep you from being A-tier. Games here go for a lot of stylistic DPs that are awesome when they connect, but when they don't, you basically end up in a corner grinding for obnoxious amounts of time, having poor fundamentals in gameplay, thin-story moments, thin-characters, or something else. Strong supers are great and all, but if you have no grasp of fundamentals, you're gonna have to rely on Burst-cancelling and hoping you can make the player forget they nearly got wrecked by an A-tier's cross-up.
C-tier members are good, but they're worse than B-tier. Except, even their DPs are weak. However, what keeps them from being in D-tier is they do one thing good. Like really good. They have one good just-combo that just works and if you're feeling like showing off your skill and have OD'd these games, you could actually pull off a win against a B-tier, or a non-focused/noob A-tier player. I don't think I've ever seen someone from C-tier hang with an S-tier match up though. But who knows.
D-tier is just. Why were you made?
E-tier is where you go if you want to be robbed. Games here actively
hurt you. They look good but they're a n00b trap. They exist to take your money and run. Best to just watch these from afar. You're also here if you're dead because you got phased out. Sucks but that happens.
Hope this helps people understand how to play this franchise. XVI is looking promising, and I really can't wait to see its combos. Really looks like it'll at least be A-tier but given who's designing them? Easily could be another S and then we'd have to redo all this.
Addendum. Stranger of Paradise is
high B-tier.
Almost A tier, tbh. Dark horse anti-meta that plays wildly outside the confines of what you'd expect from a FF. Comes off as mid but is
extremely viable with hard to telegraph mix ups and very few bad match ups. Only issues are it's model and hit boxes. Can be hard to see clearly and its weird graphics, textures and movements can make its cooldowns feel safe when in reality it's not. Definitely not the usual expected game but if you give it a chance you'll be solidly impressed. Fucking loved it. Highest of the B tier, by far.