I use the Tamron. Don't know about the Sigma. The Tamron is a very good kit lens replacement. Nice constant aperture lens, it's sharp and it's a good value. (I actually bought a used copy for $290). I use it as my indoor lens and landscape lens. It's always in my camera bag or on my camera. (My bag is usually the Tamron 17-50, my 50/2.8 macro, and then either my 50/1.7 (for low light), or something with more reach (minolta 35-105, a great outdoor general use lens, my 70-210/4-- outdoor portraits, and semi-lowlight telephoto, or my Tamron 70-300 for outdoor reach).