The 17-55mm EF-s is the best choice for a crop body, its better than the old 24-70 on a crop, and has IS.
I had 5 different 24-70 L lenses, none were all that good, and all were less than stellar on a crop. Its a roulette game, if you get a good one, it is pretty sharp, but even then, they all have curvature of field, so when the center is sharp at wide apertures, the edges will be out of focus. Its a property of the lens, not a manufacturing variable. At smaller apertures, the effect is hidden in the depth of field.
We are hearing that this has been fixed in the new lens. You will like the IS of the 17-55, and it is the correct focal length range for your camera. Borrow or rent one and try it.