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?
If you want to hear some discussion about what people like about it (and don't care about spoilers), Abnormal Mapping has a pretty good episode.