FFX-2. Simply because Yuna's growth as a person in X-2 blows Yuna in X out of the water and I'll always die on that hill. I don't consider it to be the best game in the series (story wise, X is obviously a better crafted and well told story) but it is my favorite. There is a lot to criticize the game for: there's sexualization, faux feminism,
the director of the game is
a known creep which seeps into the game itself (ex. things like the massage Leblanc mini-game), and I could probably write an essay on how despite being a 'female-led' game, woman don't hold any real, political power in Spira (all the major factions in X-2 are led by men even though in one of them, a woman is doing the real work and should be the leader but I digress). It also rubs me the wrong way how after Yuna has her little 'adventure' in X-2, SE was quick to revert her back to how she was in X for FFX-2.5 - both personality wise, career wise, and even design wise despite it not making sense for the character to do so. They basically went back on her own growth, a girl growing into an outspoken woman, and it was kind of insulting for them to do. Anyway, the point here is that most criticisms towards the game don't address any of that and tend to be very shallow and surface-level instead. In my 10+ years of being in online video game spaces dominated by men, any discussion on this game usually boils down to men either not liking that Yuna's not a quiet, shy waifu anymore like in X or men thinking they're being progressive by shitting on it when it's not helpful at all.
A lot of the things that people put X-2 down exist in pretty much every FF game too yet it gets more flack for it because it's branded in a more 'girlier' package which is harmful but people aren't ready for that conversation. Outside of Yuna's development, it was also really cool to revisit a world that was going through a major change and seeing how people adjusted to that. I thought it did a pretty good job of tackling how not everyone, especially older people, would be willing to let go of the past - even when knowing that it was all a lie - while younger people would be a lot more open to radical changes which would create a divide. The music (Yes, even the 'Jpop' people crap on) is good, Eternity ~ Memory of Lightwaves ~ is probably one of the best tracks in the entire series, and while the story is serviceable (I blame Toriyama for its faults and the lack of focus on things that should actually matter), there are some legitimate great moments in it too: Yuna meeting Shuyin and Yuna telling Nooj his plan sucks for instance.The dressphere system is great, the combat is snappy and fun, YRP have great chemistry with each other. So yeah. Probably a deeper answer than expected for this thread but I rarely going into my feelings about this game. It's a fun time.
Stan FFX-2. Stan Yuna.