I just love to come here and gush about a Sigma lens....especially when it's better than the Canon counterpart....You can just feel the "L" Groupies getting nervous tics...they try to express their opposing opinion (...the "rendering" in the "L" is more to my liking...) with tact...but you can just feel their indignation right thru your keypad.....I guess I don't understand the Fanbois groupie thing....but it is entertaining. How dare you sir? ... don't you know that there is a commandment that says "thou shalt not question L supremacy"?
My only beef with third party lenses is poor resale value, which of course stems from people's ignorance of third party lenses, thus triggering a vicious cycle.
So if the 35A and 35L were both the same price I'd go for the L. I've used it briefly, and while the Sigma is probably better, the 35L is amazing already. But I won't pay $ 500 for that L ring! I actually tape over the L rings on my lenses.
But not only the L fanboys are vehement against Sigmas and Tamrons. I was shocked how Ken Rockwell snubbed the excellent 18-35mm (even he had to agree it is optically superior) and advocated not in favor of an L but all the EF-S lenses! Of course, he recourses to simply lying when comparing the 35A's build quality to the 35L's. Without batting an eyelid, he says the Canon has a metallic body and the Sigma has a cheap plastic body.
And in both Sigma reviews he holds being sharp as a bad thing, saying these are sharp because they are built for amateurs, who care only about sharpness! Lol! So to build a lens for pros, Canon and Nikon deliberately build non-sharp lenses.