Looks like these days, one of the better lenses is the Sigma 50mm f/1.4 ART. Roger at Lensrentals tested a number of samples, and even the WORST-performing Sigma was better than every,single Canon 50mm f/1.2-L he tested. He tested seven each of the Sigma 50 ART, Canon 50/1.2-L, and seven of the Zeiss 55mm f/1.4 Otus. The Otus in not a 50mm lens, but 55mm, and is priced at $3,990. The Sigma is $995. The Canon 1.2-L is about $1619. The Sigma performs significantly better than the Canon 1.2-L lens, but then, it is newer, and is Sigma's second effort aimed right at the mighty 1.2-L; Sigma also had an earlier 50mm f/1.4 lens, priced significantly less than this new ART model, and it too performed better than the Canon 1.2-L, with significantly less chromatic aberration and was a little bit sharper too, back a few years when that lens was I think $499 or so. It's interesting that as Sigma is making significantly better lenses, they are raising their prices significantly above the low-rent neighborhood they used to be in.
LensRentals.com - Yet Another Sigma 50mm Art Post
A nifty review of the Sigma 50 ART against the Canon 50/1.4 EF (and some Sony 50/1.4 ZA samples) is found in this unusually-styled review done by a Korean site.
Gear for Image :: Sigma 50mm f1.4 DG HSM Art Review