I have had my Nikon D5100 for a few months now and love it. I'm really wanting to get an all in one zoom lens for it. I'm looking at the Sigma 18-250 and the Tamaron 18-270. Has anyone used either of these lenses and are they decent? I know you are going to compromise some sharpness of the pics by using an all in one lens. I'm not a professional photographer but still want a decent lens.. Any feedback?