I have the 28-70, my partner has the 24-70. I've done comparison shots with both, and while the 28-70 is an absolutely fantastic lens, AF is super fast and its pretty much sharper than any lens i've used, i have to hand it to nikon, i have no idea how they did it, but they really did better it with the 24-70. While i would say AF speed and sharpness are pretty much identical, the 24-70 defiantly provides crisper images. I think it has something to do with the way it separates in focus objects from the bokeh. This might have something possibly to do with different design aperture blades? Or maybe its the nano coating, but there is a difference between the two lens at wide apertures.