« on: August 04, 2012, 08:37:51 PM »
I think in your particular case the 24-105L is the clear winner. If you follow the suggestions of the other zoom lenses, you're stuck with APS-C and can't go FF.Except you can always sell the EF-S lens if you upgrade...and in the mean-time (which if he can't get another L lens for year, probably means at least a year if not longer), you've got a lens that is better suited for the body he has. 17-55 on APS-C covers landscape through the early end of portraits. The 15-85 would cover the full range he'd want, but, I'm not sure its worth the sacrifice of the extra stops of light.
Get a used 17-55, they go for $750-800 on the used market, and if you switch bodies, sell it for about the exact same price. Or, just as likely, find someone with the 24-105 and trade with them.
The difference between 17mm and 24mm is pretty significant, especially for landscape work. And the difference between f/2.8 and f/4 can be significant in indoor lighting. So why pay as much, or more, for something that would limit most of your photography?
Better suited for what? Certainly not the question he asked.