Slum,
Let's not factor non-agnostic software backends into your argument. PhysX is, and always will favor nVidia hardware. I know the latest iteration has become more CPU-friendly, but it still doesn't support offloading the processing to a non-nVidia GPU.
Currently, I only go to AMD for their GPUs, since their CPUs have been of inferior quality to Intel of late. So that's right, I'm running an i7/AMD build.
Overall, I'd prefer to stick with the underdog, because I want nVidia to stop making general products (like the Batman: Arkham Asylum games) require their own graphics card for the "ultimate" gaming experience. You want to provide the ultimate gaming experience? Then don't be an anti-competitive dickwad.
I mean, back in the day, I actually considered getting an Nvidia GPU to go with my 5870 for the physx processing. Then I learned that nVidia locked that capability out in the newer driver releases - which just utterly and completely convinced me that nVidia was not interested in the advancement of the gaming hobby as a whole, and only in their own bottom line.
Seriously, when someone sells you a Chevy, and you want to stick a Ford engine in it, they tell you that you can't do that. How would you feel?
This is actually a law on the books in one of the States...I forget which. Also, I used to be an nVidia user, but they drove me away when it came out that they were doctoring benchmarks back in the early 2000's. I have a strict policy of not giving businesses my money when they employ highly questionable practices.