I've had both 17-55 and 24-105 from the beginning and I'd say personally that the 24-105 is by far my most used lens. At it's wide end of 24 I don't find it to be particularly pleasing but a little further on and to 105 it's really good value for the prices it sells today. 17-55 is OK but I don't think it's as good as the praise people seem to be giving it lately, I don't consider it L level quality as some do. Personally I think a 24-105/ 16-35 combo is best (or the 17-40 IS if you need IS), then if you want to go really wide pick up one of the Tokina ultra wide zooms to fill the gap (I don't find them super pleasing either, but they do the job well enough for a good price). If you really want quality and light, shoot with primes (that's what I do if it's a requirement).