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Really depends what you are going to use it for and at the end of the day they are all good lenses.
If you are going to wonder about with the camera a lot then the 24-70mm is quite a heavy lens but it does have a 2.8 aperture which is handy in low light and gives more control over DOF.
The 24-105 is F4 so does not give the same oportunities with low lights or quite as much control with DOF but it has a good zoom range but does not cover the wide end very well as with the previous lens.
Remember with the crop factor of the 7D a 24mm lens is equivalent to 38.4mm (FOV).
I have heard good things about the 17-55 but then you are restricting your zoom range.
I have a 7D and am more than happy with my 17-85mm that came with it as a general purpose lens for Zoom work I have a 70-200mm F4 which is superb although I should have gone for the IS version. For portrait etc I use my EF100mm Macro and 50mm f1.8 (bargain at under 100 notes). I also have a Sigma10-20mm for wide angle specific photos.
So really comes back to what you are going to photograph most of as to which lens will be the most beneficial.
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