Through what I have tested at 17mm F4, sigma 17-70mm is the sharpest and second is the canon 10-22mm, the last is the kit lens. Whereas 17mm at F5.6 & F8.0, I can't differentiate visually any difference between 3 lens at 100% crop. I am very lucky to have a sharp kit lens but a pity that its too short for me. Though is not very fair to compare this three lens because of its different catergory, however I wanted to say that sigma 17-70mm has a very good quality in sharpness. Then again my kit lens isn't bad too.