|I can't give you any feedback on the Sigma, but I bought the Canon 18-135 a little under a year ago. One of the best budget lenses out there IMO. It's nice and sharp at all focal lengths. The zoom range is big enough to cover most of what I need (Which is why I seem to be doing so many challenge entries with it), but narrow enough to maintain nice image quality across the board. The only thing I find a minor fault is a visible amount of distortion at the short end. Easily corrected in PP, unless you are shooting for a basic or minimal editing challenge. You can see the curvature in this challenge entry:
One other minor thing that may be an issue for some people (but not for me), is the focus motor, since it is not of the Ultrasonic variety. If you like to manually fine tune your focus after auto focusing, this won't do that. It's either full auto or manual focus.
Both of your Amazon links are the same lens. It was listed separately by one of the 3rd party vendors in the Amazon marketplace. That frequently happens. If you don't mind buying used, you can save a lot on this lens. It is the kit lens that often ships with the 60D and 7D, so there is a glut of them on the used market from people that have upgraded to L glass. I paid $250 for mine from a Craigslist ad. I regularly see them going for $250-$300.
Message edited by author 2011-06-23 09:10:16.