Optically, they are very close, with a tiny edge to the Canon. I wish the Sigma had full-time manual focus, but it focuses 20% closer and is noticeably more compact.>>3988080
I looked a little bit more, and it seems that since Sigma reverse-engineered EF protocol instead of licensing it, Canon just occasionally break autofocus on some cameras when their lenses suffer too much competition. This one was a strong competitor for their most expensive EF-S lens at the time your camera was made and firmware was written, so...
All the bodies I've tested it with came out after the lens was discontinued, and they all work great. Even distortion correction and peripheral illumination have profile data provided.