Originally Posted by hieu1004
I've owned all of the lenses in question and have used them both on my 7D and 5D Mark II - so I'll give my 2 cents.
The 17-40L is a fantastic lens but is a little soft at the corners when stopped down. This lens shines on FF, so I would pick the 17-55mm EF-S lens if you're looking for one around this focal length. It's faster and has more range - more ideal for a crop camera.
24-70 and 24-105 perform very similar, but I prefer the 24-70 because of the 2.8. It really comes down to range vs aperture, what do you need? IMO, a 24mm on a crop sensor is not that wide (if it's going to be your widest lens), so it all depends on what lenses you have currently.
which is why I shoot the 16-35mm F2.8 and the 24-70 F2.8 combo. Covers the wide to long range.
I use them both on my 5DII and 7D regularly