Ken Rockwell likes the 17-40mm.
http://www.kenrockwell.com/canon/lenses/17-40mm.htm
He says, "The 17-40mm f/4 L is a better, lighter and newer lens than the fatter and more expensive 16-35mm."
http://www.kenrockwell.com/canon/lenses/16-35mm.htm
In my experience, Ken Rockwell is a knowledgeable, trustworthy reviewer.