Personally i don't choose lenses, they choose me :) If YOU are not so lucky, maybe this article will shine a light:
 
"Canon’s EF-S 10-22mm USM is one of the best quality ultra-wide-angle lenses in its range. As an EF-S model, it will only work on cropped-bodies, but the equivalent range of 16-35mm is ideal for capturing expansive landscapes, cramped interiors, large buildings or big group shots. The USM focusing is also

quick and quiet, and again the optical quality is excellent. If you own a cropped-body and want a quality ultra-wide zoom, this is the one for you."
 
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