AF is another story. I'm on my 3rd copy of this lens. The first two were erratic and inconsistent, so I returned them (which was a shame, because it's such an incredible lens).
That's the kind of thing I just don't have the time or patience to deal with.
Something has also been bothering me the more Sigma 35 photo's I look on various forums. Those photos certainly seem very sharp, but at the same time they tend to look a bit "muted," not as 3-D and popping off the page as 35L photo's. Not sure if this is contrast and/or color-rendering difference; it could even be the fact Canon 35L was/is a more expensive lens, likely being used more by professionals, presumably with more experience/skill.