Hmm. In pure graphical horsepower, the x360 and ps3 are fairly equal. The nVidia chip in the 360 pushes more polys, but has memory access issues IIRC. The Ati in the 360 doesn't have quite the pure polygon power, but does other things very well - filtering and AA at low performance cost.

If all you're interested in is high faluting graphics, they'll end up more or less equal - the PS3's big name high tech stuff is in the CPU and BRD, neither of which are going to directly affect visuals unless you like pre-rendered cutscenes.