hi there, Would you have an idea or tested those lens to tell me if the Sigma 17-70mm f/2.8-4.5 macro is better than the Nikkor 18-70 f/3.5-4.5G ED-IF AF-s DX?? I am quite happy with the sigma but I'm not sure it is as sharp as the Nikkor... I would like to know if I'd be better to buy the nikon and re sell my Sigma. thanks for advice. raf.