I have had the 17-55 before, but I sold it, I then got a Tamron 17-50 I had a good copy, very sharp pretty good in the corners too. But then I compared it with what I had previously shot, with my sold 17-55, biggest difference was the contrast of the 17-55, This made up my mind to get another used one. Well I did very well and got good one on ebay.
I will keep the Tamron for when I want to travel light. the only down side of the 17-55 is it's zize, other than that it's a great lens.