I first bought it for PS3 because of the IGN review giving it the slight edge on visuals.
I have at 50" Sony SXRD and running on HDMI 1080p.
The first thing I noticed was how much depth of field blurring was being used. Anything past 10 feet in the game started getting blurry. My gf, who normally doesn't notice anything graphical in a game, even commented how blurry it was.
I really enjoyed the game however, and the only thing that made me trade it out at gamestop for the 360 version was the fact that I encountered the freezing/loading issue about 30% into the game. Reinstalling, deleting saves, etc. didn't resolve my issue. With the prospect of starting over completely imminent, I decided to see what the 360 version looked like.
I was really suprised at how much better it looked (to me). One thing I noticed right off the bat was that the 360 version uses a LOT less depth of field blurring. It made everything look more vibrant and crisp. I was worried that the lack of anti-aliasing (which the PS3 did very well) would make it look worse, but for me the over all look was clearer and more realistic.
With the technical issues that seem to be affecting some of us, and the blurring issues, I think I'm going to stick with the 360 version for now. I'm kind of getting addicted to achievements too! Oh well, Metal Gear will be out soon...
Honestly, both versions are, for all intents and purposes, identical. However, so much can depend on what tv your running, what output, etc. The differences I noted between my two versions were VERY obvious to me, but again, it's only my opinion and I'm sure that for each opinion that states that the xbox version looks better, you'll find an equally passionate opposite opinion.
My only suggestion if you really want to know is to go to Gamestop or something and ask to look at both versions. The depth of field blurring was really noticeable to me during all hours of the day in game but it may not bother anyone else.