SIgma Drop The Big One From Japan
Indeed. Favourable hardly covers it...
I have just perused the article currently on the DPR site...in the bosses' time too... and I can see what they mean. The standard resolution graph that they do at each aperture is based upon the LPM measurements and presents as a spectrum - the red end is bad resolution and blue is good. The 50mm f:1.4 Sigma now sits in solid blue even into the widest aperture.
Chromatic aberration has been listed as so low as to be negligible and the distortion graph is flat - and stated as nothing. This is the nicest set of negatives I have ever seen on this site!
It is big - they show that it is about twice the length of an equivalent Canon lens...and I daresay that would also apply to the Nikon competition as well. And it is considerably heavier. And more expensive. All of which might be expected, given the extremely high level of performance.
If you have a full-frame or APS-C camera this may well be the best lens that you can use. Of course, the same importers would also like you to consider the Zeiss Otus 55 f.1.4...DPR seem to say it might have even a little more resolution at a higher price.
Tell you what - buy both of them. Then you can make your own tests and decide. It is the only sensible scientific thing to do. Isaac Newton would approve.