17-40 @ LACMA
For a trip to LACMA last week, I borrowed my daughter's 17-40 F4 L lens, in part to see how it compared to the 17-85 that I've been using for trips when I only want to bring one lens. Obviously, it has a narrower zoom range (and no image stabilization), and it's a little heavier, but in other respects it's far better: much less barrel distortion, chromatic aberration, vignetting, and softness than the 17-85. Many of these shortcomings can be corrected in postprocessing, but with some loss of the wide angle range for the distortion (the worst of the 17-85's defects), and in my experience it's always better to get the image as good as possible in-camera before getting to the postprocessing stage.