I had the 28-135 on crop and felt on the long end it was good but wasn't wide enough at times. I also had the tamron 17-50 and felt that 17 was good enough but I was always buried at 50mm. I've made my decision to buy a 24-105 for my 7D. It's constant F4 but sharp with no stopping down needed (for what I hear at least) but the focal length for a walk around for me is perfect. It has IS which is a plus, biggest reason for me selling my 17-50, I like to have IS.