Actually it's probably more a matter of semantics than anything else. I don't think you consider nVidia to be in competition with AMD as AMD has no desire to be in the chipset business anyway. They'd be more than happy to let nVidia take the ball and run with it.......especially if they can deliver a fast, stable chipset.
I'm of the opinion that the AMD760 is going to get mighty hard to find if the Sis735 and nForce boards turn out to be good ones. And then, there are the rumors of a new revision to the Ali Magik chipset that gives better performance. Sigh, wish I could get some confirmation on it.