Tamron AF 70-300mm F/4-5.6 Di LD Macro VS Sigma 50-200mm f/4,0-5,6 DC OS HSM?

T care about the price, just the performance.
I shoot Nikon.

The Sigma 50-200 is no longer available. You can see lens sharpness charts of the Tamron at photozone.de

If you don't care about price, go for the Nikon 70-200 f2.8 VR or the Nikon 70-200 f4 VRII. They are both excellent lenses. If you find them too expensive, the Nikkor 80-200mm f2.8 is also a very good choice.