My informal polling method uses the B&H customer reviews. I set them low to high and count how many does it take to reach 4 stars.
If the percentage is 10% or more less than 4 stars, I walk away...
Between 5% and 10% I will consider it
Under 5% I'll put it on my to buy list.
Canon EF 85 f1.8 22/1317 less than 4 stars 1.17% a MUST BUY!
Sigma 85 12/77 or 15.6% ho-hum. Now if you read the actual reviews you find that some of the dissatisfied customers have gone through the Sigma AF lottery more than once, which makes the percentages worse...
Now, if you want to see REALLY happy campers look at the Canon EF 400 f2.8. ALL 5 star ratings...