17-40 is a great UWA zoom on FF for the price. Slightly soft in the corners, but acceptable and distortion is not that bad. It also takes 77mm filters, which is great since many zooms at longer FLs do the same. I do prefer the 16-35 II however due to being faster, sharper at the corners, better microcontrast, better distortion control and creates beautiful starburst. If you do any night work such as the milky way that extra 1mm and extra stop is definitely beneficial. It's also a great PJ lens as well. The main downfalls are of course price and many are not a fan of having a 82mm thread regardless of what filter system you use. Of course the main thing you need to consider is what you shoot and the intended use of the lens.