As someone who long, long ago sold camera equipment at a decent quality location, I approach this one a bit jaded. (Hey, it put me through college, okay?) Personally, I don't like what happens when you combine a wide angle lens with a middle range telephoto. I tend to notice the curving of the edges (my hobby was architectural photos) where a straight line would bow at the ends. I personally own a 21mm, 28mm, 35, 50, 120, 400, 1000, and a few zooms in the 80-200 range including a f1.6 (can you say "big hunk of glass?"). With that being said, the lens which is on my camera 85% of the time is a Tameron 35-80mm with an incredible macro. I LOVE THIS LENS! From being able to shoot detail work from 4" away to shooting landscapes, this baby does it all for me.
If you're shopping where you can actually mount and try the lens on your camera -- put a lens on, focus, and then change the zoom without changing the focal point. Do you need to refocus? If so, pass on the lens. My 35-80 Tameron is just so sweet, I almost can't stand it.
Servants of Evan