Gamespot would tell you they are about the same
More at the link with comparison photos...A solid year's gone by since we ran our last Xbox 360 vs. PlayStation 3 graphics comparison. The differences between the Xbox 360 and the PlayStation 3 have diminished with every passing batch of games, but some variation still exists between the two machines. Our first graphics comparison between the two consoles showed that the Xbox 360 looked better on most of the games, oftentimes drastically so. The second graphics comparison showed that the PlayStation 3 looked nearly as good as the Xbox 360 in some games, and actually looked better in a few as well. Now with both consoles well into their respective life cycles, developers have had plenty of time to figure out the nuances required to code beautiful games. With our third batch of games, the two machines seem evenly matched. The two trade blows on various games, each with its own set of advantages.
I think this is what happens when you don't necessarily have a clear winner - devs end of focusing on the common ground between platforms rather then necessarily spending endless type optimizing.
Between this, XBL, and the speed of the blu-ray player - I'm glad I stuck with a 360.