The 360 can handle 1360x768 through hdmi so it's slightly sharper. Never found an option for that on PS3 - just 720p. Not much but it is noticeable.
Probably the TV I would imagine.
Edit: farking forum backup
Edit 2: @DL yeah like last gen where most games are 720p the advantage of a higher resolution is a slightly crisper picture or the tv/console will downscale umm upscale whatever etc..
Just like an old PS2 with component cables even though it doesn't support HD modes (even 480) you still get that extra little oomph from it on a current screen. Unless more games were released in 1080 the last few years as I'm not that current anymore.