For me it's
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Final Fantasy Tactics
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Final Fantasy VII
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Final Fantasy XI
The three games I keep coming back to in the franchise.
Tactics has the best writing imo as well as gameplay.
Visually speaking VII's aesthetic and music are peak FF.
And then when it comes to getting lost in the lore and world of a virtual game, I like XI.
Granted all 3 share similar themes like good writing, music, gameplay, etc. but those are my standouts.
How about you?
Final Fantasy XIV, VI, and (give me this for nostalgia purposes) IV.
I know IV wasn't particularly sophisticated, but some of the music still holds up, and the vibes of some key moments still resonate with me, such as Cecil's final test to become a paladin.
https://www.youtube.com/watch?v=T0QDhNgLGZk
IV is a really good pick negl and if VI didn't exist I think IV would be my favorite.
The final battle slaps too. It was revisited in FFXIV!
https://www.youtube.com/watch?v=GmsSMtswgwA
I found a YouTube link in your comment. Here are links to the same video on alternative frontends that protect your privacy:
The best part of the Deltascape raids imo
The best part of the Omega fight is when it sounds like the singer is singing
HOLE 
IV is good. We have to keep in mind that this was the first Final Fantasy game on the Super Famicom hardware, so they were trying to figure out what that new era of the franchise would be.
FFIII in Japan had more gameplay variety and options, but FFIV started a trend of cinematic emphasis in the series that is still part of its ongoing appeal now.
I found a YouTube link in your comment. Here are links to the same video on alternative frontends that protect your privacy: