i saw both versions running at the same time:
there are 2 differences, one scores for 360, the second for PS3:
360: A little bit brighter colors. there are a bit more intensive on 360, which looks actually a very little bit better.
PS3: It can load various details faster as the 360, and show them earlier, and you can see them (a VERY LITTLE bit) better in the distance. (the one picture with the stones at the ground , completely missing on the 360 was the only extreme exception i saw.)
a small point: you need 700mb space for the game on ps3, its nothing big, but i think that made it possible to score in the detail-case.
so its not important which version you get, because you wont see any difference, if they arent running side at side.
(things used: my hdtv, his tv (same as mine), my ps3, my 360, my PS3 prototype copy, his 360 Prototype copy.)