Hi Guys and gals, was wondering if anyone of you have experience in both these 2 lens? I'm planning to get a zoom lens that can be versatile in Low Light and is also sharp enough as compared to the Canon 17-55mm IS. The lens I'm looking at will be used more in indoor events. Cost wise, these 2 lens are actually way way apart but, how about sharpness, color and contrast? Any comments from the experts here?