Just got my 3 copies of Sigma 35. 2 of them has the focus squeaky issue that sounds like a 15 year old car's belt in cold weather (1 of them did not focus probably with any MA, the other one I did not even bother). I already sent them back. The other one just does not focus properly. I can MA to get it to focus fine when the camera is static. But the minute I move the focus chart by 5 or 6 feet, the lens requires a different MA in the opposite direction! Unbelievable, how hard is it for these guys to get this right. This in total makes 12 Sigma copies I tried over the course of 3 years and every single one of them (not kidding here) had similar issues.
That being said, the lens IS sharper than 35L, significantly. Especially in the corners, wide open, it destroys 35L. But unfortunately that accomplishment is utterly useless because there is no way I can reliably use this lens.
One other thing to note is Sigma has significantly more vignetting than 35L. Most pictures taken wide open will require post processing.
I will post some pictures tomorrow and do a deeper analysis as I think it might be useful to other people who might be in my shoes.
Edit : I know I said I'll post some pictures tomorrow but I could not help myself and decided to post 2 pictures to show how bad vignetting is, I think this is ridiculous.