I replaced my 18-135 mm, with 15-85mm IS USM f3.5/5.6, IQ is very good, please take note this is not L lens, but the IQ you can check it by yourself. The minus thing is the variable aperture 3.5-5.6, not like 17-55mm f2.8 IS USM, fixed aperture (this one also not L lens).
I can say 17-55 f2.8 IS...