I used Tamron lenses for years until the D300, then I went Nikon glass all the way. One of the big differences is that the AF-S lenses are so fast compared to Tamron. The sharpness is noticeably better. If you are going to spend upwards of $5,000 on a canera get the best glass, which is Nikon now. The 24-70 is a dream lens. Just holding it you can tell the superior quality.