I currently own a Sigma 10-20mm to cover the super wide end, and a Canon 70-200mm F/4 to cover the super telephoto.
I'm thinking of adding a walk-around lens to my arsenal. My current thoughts are either a Canon 17-85mm F/-5.6 IS, or a Sigma 17-70 F2.8-4.5.
I am attracted to the 17-85 because of the IS / low light capability, however I think the Sigma is probably a little sharper, has better build quality, and is slightly smaller (and slightly lower cost).
I'd appreciate your thoughts.