Well i was thinking about selling both of my 18-55 IS and the 55-250 IS since i barely even use them and get a Tammie 17-50 f/2.8. I was going through some in the photo archieve threads and making a decision between the tamron 17-50 f/2.8 or the canon 17-55 f/2.8. is it worth spending 400+ more on the canon than go the tamron way? Right now i have a nifty fifty and the sigma 10-20mm and thinking of selling both the 18-55 and the 55-250mm soon. i want a nice sharp walkaround/portrait lens and also good at taking some candid shots.