I only have a 17-55 2.8, 18-105, and 10-20 Sigma as DX lenses and as a walking around lens, even for portraits the cheap plastic 18-105 has been a pretty good lens and some of my most requested prints used that lens. The Sigma 10-20 is a lot of lens for the money if someone is into Dx ultrawide angle..tough, sharp and manageable distortion.I even use it for people shots for special effects like 10mm shot of my GF on the roof of the art center next door where I was no more than 24 inches from her but got head to toe with great color and contrast.
Here is an example of an ambient light portrait of a guy flirting with his waitress 10 ft away in a Warsaw Poland cafe using the lowly 18-105 at 105mm at hi-ISO, D90
I used to have a 35 1.8G and thought it was a very competent lens and better on Dx than the 50 1.8G..also an excellent lens but too long on Dx to be a walking around lens with a field of view of 75mm.
My 17-55 2.8 sits on the shelf until I can find someone to buy it. Ater getting the 24-70 2.8G, which has much better IQ, color, and contrast.
A favorite lens on Dx, however, is the 70-200 2.8 That is the second lens most people get after deciding to invest in quality glass. It is popular for a good reason.
For people shots, it is hard to beat the 85 1.8G for IQ and value around $550.
None of the superzooms are that good for IQ but they are very handy for low weight travel shooting.
I have a pretty good assortment of Fx lenses now, with 1.4 and 1.8 primes and 2.8 zooms but those take a real investment and are not needed until someone decides which specialty they pursue and seek top glass.
The main reason I liked the 18-105 so much was that it was small and light, so a camera and 1 lens could go with me all the time and most shots you really want, are by stumbling onto opportunities. The lens and camera you have with you are the best ones.
