Without taking money into account, I would say the 24-70 II without a doubt, every single time. I primarily shoot weddings, and unlike the other photographer who says he rarely shoots @ 2.8 (Not saying he is wrong, just a different shooting style) I find the need to shoot wide open quite often. Not during the formal portraits, of course, but during the ceremony an extra stop would be amazing.
I say this as a current owner of the 24-105L, and I personally avoid it like the plague during the ceremony. I stick to the 70-200 2.8L IS II or primes, as I am not satisfied with the sharpness or the aperture of the 24-105. The 24-105 is a fine lens in its own right, as it is cheap, constant aperture, built better than the 28-135, features IS, and it a great walk around lens with satifactory (Not great) image quality, but if given the choice, I would go with the 24-70L II.