Ken Rockwell [Tested on Nikon variant]
This is an optically superb lens, but there is far more to a great photo than a sharp lens. It has to be light enough to enjoy taking with you. This Sigma is fantastic, if you don't mind carrying it. [...] This Sigma is ideal for people who shoot with tripods.
[Tested on Canon variant]
It is distinctly large, heavy and expensive for its type. However this is more than made up for by its fast silent autofocus, solid build quality, and absolutely outstanding optics. Overall it stakes a very serious claim to be the best autofocus 50 mm prime on the market right now.