To sum up, it seems like Sigma is much less reliable than canon here. 35L has been tested for more than 10 years and the only real problem is CA when wide open, though it's not often seen. The AF is more stable on canon's side.
Seems like I'd better remove CA when retouch a pic... yeah, 35L is my choice, for sure.
Have we been reading the same thread posts? I'm gathering it's actually trending towards Sigma. At best for Canon, it's 50/50.
I've used both on my 5DM3, and there's no comparison - I love my Sigma.
I guess that's harsh...Canon is good, but Sigma is great.