Of those I've played, I would rank atmosphere as best in VII, then XIII, then VIII. I've not got far enough through III, IV or IX to say much for them. It was hard for me to get into the atmosphere in XII because I never really got too attached to the story, which for me plays a massive part in the atmosphere.

VII trumps the lot somehow. I'm not exactly certain how it did it, but every movement through every area (arguably Costa Del Sol and Wutai excepted) felt like it should have felt in the story. When you were in the slums, they felt like slums. When meteor hovered in the sky, you felt the threat it posed. When you got the Highwind, you felt the exhileration at the freedom it gave you with that wonderful music that accompanied it. I would say that the music plays perhaps even more of a part than the environments do, now that I think about it. It's perfectly done.

XIII has atmosphere because of very different reasons. Sure, the music and the environments are good. But Basically, the storyline and the characters and the NPC comments. You felt like a refugee every bit of the way. People often criticise the fact that story is so linear and how you can't go back to previously visited zones, but despite the damage this made to gameplay, it did build on the atmosphere. You were in a world where you could not stay anywhere for long, you were on the run, and run you did. Some environments didn't really give you the feeling it could have, but luckily the characters were able to keep you in the atmosphere of a refugee. You felt the fear of the people when the purge was in full swing, you dragged yourself through the dirty dustbin of Cocoon, you went through all-this-dampness-is-damp greeneries, you snuck your way around people as they went about their business, you got caught and caught again, you kept running and you eventually escaped and felt the full thrust of freedom when you finally got to Pulse, and then an entirely different kind of atmosphere held you there. I liked it.

VIII had atmosphere in certain places, but not so much atmosphere in the game as a whole. I would say that every town and location had it's own unique atmosphere in this game. Deling City, Fisherman's Horizon, Balamb, Esthar... you could feel each differently.