mwsilvers wrote:
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While I have a few lenses that are a bit sharper overall, none of them provides the flexibility of the 15-85 range.
....................... With its 15 mm at the wide end, I rarely find I have need to use my Canon EFs 10-18 mm ultra wide lens.
Getting back to the OP's original question, I would recommend the Canon 10-18 mm if she would rather capture a single ultra wide angle image instead of stitching a pano together.
Stitching panos is cool for stationary subjects. The 10-18 might be acquired with landscapes in mind, but unlike stitching it invites the user to use it in crowds and other active situations. It also makes great video (STM is quiet).
The 10-18 inspires. I do recommend increased use of live view for static scenes. SLR finders can be deceptive with ultra wides. Viewing on the rear panel is more revealing of odd things that occur with extreme wide angle foreshortening and angle of view.