I have posted this same question over at dpreview so if anyone has answered there no need to answer here.
I have some extra dollars left from vacation and I can purchase one of these lenses. The two seem to be rated very good on sharpness. I know the 17 will give a larger field of view. I have a 5Dmk2 and a 60D. My concern is the large bulging glass of the 17 and flare issues. I also have a 12-24mm Sigma, it has bulging glass also, and I know that flare can be a problem. I just returned from a trip to Arizona and Utah and used my 24-70 l the most, so I could most likely live with the 24. If anyone has first hand experience with these lenses could you let me know your feelings about them?