You haven't said what kind of photos you like taking.
The 17-85mm goes much wider than the 28-135 - remember if you're mounting them on something like an EOS 400D, you'll effectively be multiplying their focal lengths by 1.6 times.
So if you want genuine wide angle coverage, get the 17-85mm. If you're not bothered about wide angle, but would value being able to zoom-in a bit more, then go for the 28-135mm.
Both models have IS, although some older 28-135's may not.
I haven't tested the 28-135mm, so can't comment on its quality.
If you're after a good general purpose lens for the Canon bodies, I think it's had to beat the 17-85mm. Our full review is here:
http://www.cameralabs.com/features/Cano ... s_upgrade/
Hope that helps!
PS - you could also go into a shop and try both lenses to see which coverage looks more useful to yuor kind of photography.