I used the 17-40L on 7d for a few years as a general walk around. the IQ on crop is very good.
It is very small and light, the AF is super quick and accurate and its close focussing on crop yields some decent enough macro shots.
However 40mm f4 is not fast or long enough to create any decent subject isolation. I wasn't really using the lens for landscape purposes so I ended up selling it and got the 17-55 2.8 IS instead.
I cannot comment on the 15-85 but I can say that the 17-55 is a lovely lens. lightning AF, extremely accurate. Very sharp @ 2.8 (except for closest focusing distance where some residual aberations creep in, but @ the closest focussing distance you need to stop down anyway to create usable depth of field).
The 17-55 is a dust hoover and after a year of relatively light use my copy is full of dust. but I've never noticed any degregation in IQ.
I would say if your photographic focus is at the 17mm end, and you don't mind using a tripod in lower light, go for the 17-40m as the build quality is better, its weather sealed (if you add a filter) and can serve as a full frame lens should you upgrade.
Otherwise, if you want it for the longer end. I would get the 15-85 or the 17-55 f2.8