... their lens comparison tool is an excellent resource
...if you only shoot in lighting equivalent to a dimly lit warehouse.
Their Measurements are useful, their Scores and the rankings which are based on them are generally meaningless (except in warehouses ).
I should qualify that be saying their Measurements can be useful, when they're correct. They weren't for the 70-200 II, but they defended them until they silently updated them. Their measurements of the 17-40L are also suspect, as they apparently show it's as sharp in the corners as the center wide open, and sharper at f/4 than the 16-35/2.8L II stopped down to f/8 - I don't buy either of those.
Well, they did figure out that it's a great travel lens (at least they got that right), something that is also clearly stated on the Canon Europe website (and I agree!!) Doh!: