I've used the 17-55 and it's a wonderful lens on DX, but I would expect the 24-70 to perform even better, as it's a top of the line lens, and is much newer. Nikon's alphabet soup comes to mind. Nano Crystal Coating, and all of that gibberish is on the 24-70, and not on the 17-55. Though, if you shoot DX, just get the 17-55. It's sharp, sharp, sharp, and performs great. The 24-70 did seem to focus faster, in my case. Though I was using a very beaten up 17-55 and a brand new 24-70, so I can't really be sure if this is true.