1) PS3 is one blu-ray disc, while the 360 is 3 DVDs. I don't view this as overly significant, but some people hate switching discs.

2) Squeenix has confirmed that the audio and video of the 360 version will be compressed, while that of the PS3 will be uncompressed. I've seen talk as well that the 360 will output a max of 720p, while the PS3 will be capable of 1080p, but I'm very unsure about that. I believe the Japanese PS3 version can only do 720, so I'm not sure why they'd change. Anyway, if 1080p is important to you you might want to check further once it's released.

So yeah, there are no real differences. Even a little bit of compression doesn't necessarily mean that graphics will be negatively affected. There are loads of examples out there where the 360 version of a game looks better, despite the technical superiority of the PS3. We'll have to see.

If it were me, I'd decide whether 1080p was important to me and, if it was, check on release day to see if the PS3 version could do 1080p. If it wasn't important to me or I found out that the PS3 version could only do 720p, then I'd just buy the game for whichever console I preferred playing on. Minor technical differences are unlikely to affect the game in noticeable ways.