I thought the Xbox version looked a bit sharper with more vibrant colors too (this was before the patch) but it was only slight. My friend and I also noticed the cars sounded a tiny bit better on Xbox vs the PS3... a little bit meaner, as it were.
These were extremely small differences though, most people wouldn't even notice.
I also prefered the Xbox 360 controller, which is godly for this type of game.
But I bought it off PSN despite all that b/c having the ability to play it off the Hard Drive trumps everything.