To critical reader Roger's testing and dxomark agree 1:1 on the FE 35/1.4 ZA in sharpness comparison to competition from Sigma. Sigma 35/1.4 is way sharper throughout the frame on open apertures (dxomark link below) and even stopping down the 2x more expensive Sony never catches the Sigma. Sony is not a bad lens, it matches Nikon 35/1.4 both in Roger's test and dxo, but the Sigma Art (and new Canon L as it is neck to neck with Sigma) are on way another level in terms of sharpness. For any normal person any of these lenses provide superbly sharp results (
and with A7R II it is sharper than any FF camera+ 35 mm lens combo was before 36 MP Sensors came out), but as enthusiasts in a gear forum we tend to be interested on how these products stack against each other in different qualities.
Check dxo link below for comparison of Sony, Nikon & Sigma in 36 MP AA-filterless bodies. Click Measurements => Sharpness => Profiles for sharpness graphs, there really is no contest.
Sony Carl Zeiss Distagon T* FE 35mm F1.4 ZA on Sony A7R vs Nikon AF-S NIKKOR 35mm f/1.4G on Nikon D810 vs Sigma 35mm F1.4 DG HSM A Nikon on Nikon D810
In many of these areas Sony shines. I like colors from Sony Zeiss generally much better than the others, the bokeh is arguably best in 35/1.4 ZA (drop sharpness and nice/smooth bokeh becomes easier to achieve) and for example for environmental portraits Sensor-focusing Sony with Eye-AF murders the competition in focus accuracy/repeatability.
Then again, personally I see no reason to combat a tester's credibility if one does not care about what is tested in said test. Roger Cicala is as credible as tester's go. His/Lensrental's testing provides hugely valuable and unique data to photo community as things like copy variance are tested practically nowhere else.