The Sigma 17-70 apparently has some quite severe distortion, the 18-50 does indeed do a much better job. That the Sigma 18-50 doesn't go down to 2.8 isn't really a problem, I have a Nikon 35mm f/1.8G for most of my more pronounced depth of field shots, as well as the ones taken in the dark. I really need the low-end width for landscape photography though.

The question is, is the Sigma 18-50 worth double the price of the Nikon 18-55 Kit Lens? I just keep hearing that it's a good lens and it's making me irritated.