I've owned the Sigma 35, 2 copies of the 35/2 IS, and 2 copies of the 35L.
I would take exception with this article stating the 35/2 IS is "sharper" than the 35L. Wide open, yes. But the 35L is much sharper @ F/2 especially in the center and vignettes much less.
As far as 'clinical" sharpness, yep, the Sigma has that, along with a brownish tint that makes up the character of the lens. The 35L IMO just has the best bokeh, color, contrast and rendering. If I took 100 shots with the 35L and the 35/2 IS, the latter might result in 100 really good photos, but the former might have 8-10 amazing shots. The 35L is still the king of the 35's.
Sigma = sharpest
Canon 35/2 IS= light, IS, better AF accuracy than the Sigma, plenty sharp enough.
Canon 35L = best build, fastest and most accurate AF of the three, best color/contrast/bokeh. Really sharp around F/2 and beyond, and F/1.4 is usable.
I have to disagree, my 35mm F2 IS walks all over the L lenses i have owned including the 50mm 1.2L it has brilliant bokeh and is sharp and contrasty to boot , it can also take an amazing close up ....
It may be that i have an extra good copy granted but it certainly is good. I would not swap it for a 35L
example shot : 5Dmk3 35mm F2 IS, F2 iso500
Wedding Photographer Durham Darlington Teesside Newcastle York
I agree regarding the bokeh from the 35 IS. Great shot, by the way. It is very useful as a pseudo macro in the field, particularly when you want to include a bit more environment.