[UPDATE] Rumor: Final Fantasy XIII timed PS3 exclusive outside of Japan
At the Square Enix press conference they have stated regarding the xbox 360 version of the title
"The game will first be released in Japan, and then the localization process will begin and the game will be developed for the Xbox 360."
Now seeing as the game won't be ported over to the Xbox 360 until after it has been released in Japan, it does seem that the PlayStation 3 version will be released first, as porting the game over will take longer than localising the PlayStation 3 version.
Update - Rumor Debunk
It has been confirmed that both the Xbox 360 and PlayStation 3 versions will be released at the same time in Europe and USA
