Comparing X360 developed games to their PS3 ports doesn't really make alot of sense, especially given that even GPU shaders need to be customized and adapted.
I think its fair to say the games developed on one platform, and ported to the other are going to be better on the first platform. With that, the X360 is often the development platform of choice for 3rd party devs, for a variety of reasons. Putting the two together doesn't make for X360 > PS3, however.
Comparing exclusives is really the only way to go, in this regard, and the PS3 exclusives *are* superior to the 360s exclusives, or so state a large number of professional reviewers, with comments like "best looking game of this generation", etc. (MGS4, Uncharted, Heavenly Sword are good examples). Cross-platform games are often (not always, as in the cases of huge titles like Oblivion, DMC4, and GTA4, to name a few) perceived as being better on the X360, by the reviewers.
On the flipside of that point -- 3rd party X360 game engines are more developed than their PS3 counterparts, and this may remain true for at least a few 3rd parties, throughout this generation. Then again, it may be that the PS3 is harness ed well by some 3rd parties, and their X360 engine just cannot hope to match it.
Performance, and appearance, is game engine specific, rather than platform specific, when comparing the HD consoles. That's that.
