A top pick
I carefully researched and read all the reviews of available super-wide zooms before settling on this one. There is a lot of choice now, and each lens seems to have its own strengths and weaknesses. However, in my opinion, this lens is still a standout.
The construction quality of this lens is far beyond what one would expect for a lens of this price. It feels incredibly solid, like the high-quality prime lenses of many years ago.
Both the zoom and the focusing ring are very smooth-operating, and perfectly weighted. Focusing is extremely fast, accurate and silent, and full-time manual focusing is possible. The lens has a window with a distance scale.
Distortion is pretty well-controlled, for a super-wide. There is some noticeable distortion at the widest setting, but of course it is correctable. The overall image quality is quite good for such a wide lens, especially at the short 10mm setting, which is where this lens will likely get the most use.
The front lens element has a significant convex curvature, but fortunately Sigma has designed the lens so that you can attach a filter. The front is non-rotating so you can use a polarizer if you wish (keeping in mind the limitations of polarizers at super-wide settings), or just attach a high-quality UV or clear filter for protection.
Sigma includes both an effective lens hood and a nice soft-sided case.
This lens is very nice to use, and when taking its price into account, is an outstanding value. If you are looking for an APS-C super-wide zoom, take a good look at this one.
The image quality while quite good, still has some weak areas. Some of the competition may offer somewhat better image quality, or a larger maximum aperture. However, those lenses will likely be inferior to this Sigma in other ways, or cost significantly more. Determine your personal priorities before making your choice.