If you like to do outdoor stuff and take wide landscapes the 17-40mm F4L would give you high quality and a nice wide viewpoint. If you are more into portraits, the 24-105mm F4L gives you the better high end range.


Question to ask back to you is how do you like your 28-135mm at the short end? If for your style it's okay go for the 24-105 because everything is very similar. If it's not wide enough at 28mm, you may want to lean toward the 17-40mm.