I considered the 15-85 before buying my 17-55. I LOVE the constant F/2.8 aperture of the 17-55.
I believe the 15-85 is a good lens but too "slow" for the money. If you want a good lens get a 17-55 or even a 24-105 (which I also own). Both are 300 bucks more but worth it IMO.
All that said....the 15-85 is still a tempting lens IF your style supports it and you're willing to use a variable aperture lens. I like fixed aperture (as do all who have used them)
I would not get a third party lens. They twist the wrong way!
I'm not criticizing the 24-105mm. But at f4 is not all that fast. and on cropped frame sensor it's not terribly wide either.
















