Can't tell you for the newer HSM model, but older screw driven one is excellent. I have compared it with Nikon and whilst AF is definitely faster, sharpness-wise Sigma is razor sharp (well at least mine). Taken a portrait photo(s) at around 50mm at F/2.8 in studio conditions with this lens and had to postprocess it later to hide tiny facial hairs that this lens revealed with damn good clarity (so to me very sharp). And they are dead cheap comparing to Nikon one. Of course given the money is no object, I would have gone to Nikkor - like its build better.