You should be looking at 2 lenses, the
DA 18-135, and the
DA 16-85
The 16-85 is wider and sharper across it's whole range, the 18-135 is good in the wide end, and still has excellent centre sharpness in the long end for portraits and wildlife ( but not as
good for landscape in the long end.)
Both lenses have many ardent and fervent users.
With all due respect to the above posters, I personally don't think a lens that only goes to 50mm is a good travel lens. And for speed and low light, a 50 1.8 and 21 3.2 are better options than carrying a 16-50 2.8 if you need fast. People constantly over emphasize the value of ƒ2.8 in travel lenses, as if you're going to be shooting in caves all the time or something. I'm not really sure what the logic is, or if it's just something they say because they bought an ƒ2.8 lens. You don't hear a lot of people who bought 18-135s saying "gee I really missed having ƒ2.8 on my vacation." To me, the 16 mm of the 16-85 is probably more useful than the ƒ2.8 17-50 type lens.