A case for your reference:
Used to have all Ls (17-40, 28-70 & 70-200), They are technically very good lenses. Only if I can make full use of them. :think:
17-40L is sharp and colours is good, but its range is a bit short for portraits, so whenever I want to shoot portraits, I need to switch lens. If not I have move closer to subject, but the subject may get distracted, composition may be the way I saw it initially.
I had problem using 28-70L because of the 1.6x crop, always cannot make full use of its range even though f2.8 is nice. Whenever I shoot weddings, I always keep it attached to my other camera(300D), but very rarely able to use it because of timing and the trouble of switching cameras and flashes.
So I sold 17-40 and 28-70 for EF-S17-85 which covers the 2 ranges of L lenses. This EF-s lens may not be able to create the quality of Ls but its range is perfect for me to shoot weddings from group shoots to portraits, just nice! IS is a bonus, whenever I shoot with ambient lighting. The only weakness is lacks DOF control, I need to drop to f5.6 to get good sharpness, so will not get nice blurred background.
I kept 70-200 f2.8 because I really appreciated its ability to be used wide open to create the blurred-background effects I like for portraits and animal shots, not compromising sharpness. also f2.8 really speeds up my shots to prevent motion blur when my subjects are moving.
Some may say, like that may as well get a 28-200 :nono: not true, unless there's a lens that's fast(wide f) and long range and sharp. EF-S 17-85mm is just right and doesn't compromise too much quality.
I learnt to make of use of the way the lens is built to function. Not the way the lens is "label" or "branded".
Its only worth it if you know how to appreciate it and make full use of it.
PS: Now selling my 17-85 for 18-50 f2.8 because really like to control my DOF.
