Any lens with such a wide focal range will be making a compromise on image quality in exchange for convenience. You would be better off to replace your 55-250mm with any of Canon's 70-200mm lenses. There are many options that would be good replacements for the 18-55mm lens. If you like that focal length, then I recommend saving up for the EF-S 17-55 f/2.8. If you don't need as wide as 18mm, then consider saving up for either the 24-70mm f/2.8L or the 24-105mm f/4L.
Canon 40D, Canon Rebel XTi. assorted Canon L lenses
Quoted Message: The 10-22 and the 24-105 are definitelly much better.
I took the Canon EF 24-70mm f/2.8 L USM in kit with the 5DMKII, since reviews gave it a marginal sharpness advantage over the Canon EF 24-105mm f/4L IS USM.
As for now, I regret it a bit since the 24-70 is very heavy and it brings the light 5DMKII body out of balance when used outdoors for general purpose shots. Also, the 70mm limit is a bit tight in studio for cropped portrait shots on a full-frame.