PS3.
I have played on both consoles on HD Televisions. The PS3 indeed had better graphics.
That is one game, all the other good games for the xBox 360 are also available for the PS3. PS3 have more good games which are not available for the xBox 360. Not to mention that you get a Blu-Ray player with the PS3 and only a normal DVD player with the xBox 360. You have to buy the HD DVD player seperately for it.
Need I say more?