I have $900 to spend on a lens in the range. My initial plan was to buy the sigma from my local shop and be done with it. Many folks give it great reviews, about half seem to have trouble with it's focus calibration. Reading reviews on the Nikon 80-200 af-s, it has overall better reviews but apparently there are alot of bad copies of it out there too, some with focus issues like the sigma To get it used for $900, I'd have to buy on ebay. Not too big a fear for me, as I use ebay alot. The bigger problem I see is that if i end up with a bad copy of the nikon, I don't have a warranty to cover it. I'll be using the lens mainly for sports, and some portraits if it makes any difference.