I don't really have one. I don't even think in those terms, much; I write about people, not cultures, although of course every character is part of the context of their culture: the culture of Spira, of the Al Bhed, of the warrior monks and Crusaders of Yevon; of the different nations of Ivalice, of the sky pirates; of the Guardian Corps and PSICOM. And all of these are cultures I've enjoyed developing and playing with (although I suppose not the sky pirates so much, yet; I should get the opportunity to do so in my Mega Flare, and the Guardian Corps and PSICOM in my half-planned future FFXIII fics), but I can't really pick one that I enjoy above all the others.
30 Days of Writing: Complete list of questions
This entry is also posted at http://owlmoose.dreamwidth.org/484217.html. There are currently comments on DW.