I am using the 24-70. After having send it in to CSC 2x for calibration, it is still soft at 2.8. It only begins to shine above 3.5. After that it is very very sharp, as good as a prime. I spent a lot of time with the CSC people over the softness at 2.8 and they really tried their best to help me resolve it. I have to say their service was way above expectations. I have come to the conclusion that it is either my copy that is like this(but I have tried a few copies at CSC and they were worst) or it is just the inherent characteristic of the lens. I tend to sway on the latter. It is a heavy lens but after a while you get use to it. In my opinion it is a great lens. If I have to travel with 1 lens this is the one I take. I also have the 17-55 but somehow I prefer the 24-70. So much for the odd FL to some. I was very close to selling it because of the softness at 2.8 but have learn to live with it, after checking out all the available alternatives. I have yet to try the 24-105, but from what I read it is not sharp wide open as well. If that were the case then it would be of no use to me having to shoot close to f5 and above to be satisfied with it. That's just me.