If you are concerned about how games are looking on your TV sets you need to understand the nature of modern day game 3D engine.
Simplifying the facts, we can say that are two kinds of 3D objects (usually there is a mix of both) one that are represented by mapping 2D textures on the polygons and this can be either offset/parallax mapping or bump mapping. The second categories of objects are handled by shaders from the GPU. The shaders will give us shadows, fire effects, enhanced lightning effects, HDR and many more.
Comparing the specs of the two consoles, we can say that PS3 has more raw power, this means that there is a better texture resolution (this means less blurry images when you are looking at an object up-close), you can have more 3D object simultaneous on the screen, you have a increased view depth and an enhanced, more precise collision detection.
Again, just looking at the specs, Xbox is having a more powerful shading GPU that will produce some nicer effects.
It's difficult to say which one is better, when I worked for UBI Soft, the idea was that the games should look the same (cost effective) but different companies may have different strategies. If can you look at one game on both platforms and you can notice a difference, doesn't mean that you can say the same for all games. It’s always bad to make general assumptions about things that you have little knowledge on how they work.
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