Lots of people are asking about the different in IQ and sharpness between the 16-35 f/2.8 L MKII and the 24-105mm f/4.0 L. They are of course very different lenses, but comparing my 2 pieces of glass, the 16-35 MKII has better contrast, colour, IQ and sharpness than the 24-105. Here's a shot I took last week of the Tokyo Tower in Japan with the 16-35 MKII.
Tokyo Tower by JEF 96, on Flickr
For a wide angle lens, it's amazingly sharp. I hope this answers all your questions.