I can say I am really happy with my 5870.
Not only is it really fast, but it also runs pretty cool and doesn't use a lot of power.
Though I would suggest you look for one with a reference
cooler (often called the 'batmobile' cooler)
Anyway, CUDA/PhysX is pretty much an attempt to control the market standards. And I won't support that.
DirectCompute and OpenCL are used by Nvidia and ATI.
Directcompute is good because it's already part of the DirectX 11 specification.
OpenCL is good because it works well with OpenGL, and it can be run by the GPU or the CPU, or both a the same time.
I think I would like to see Nvidia either open the CUDA/PhysX standards, or just drop them in favor of DirectCompute and OpenCL, and change their strategy to try and achieve low power consumption and price while still having high performance.