I chose the 24-70, but only because the price was absolutely right. Had it been the other way around, I would have taken the 24-105 in a heartbeat.
When you buy the 24-70, you buy it under the assumption that optically it is a great lens and that realistically you are buying it for the F2.8, the bokeh and the excellence gained by stopping it down. That being said, many review sites put the 24-105 and 24-70 at the same level in regard to sharpness in the apertures and focal lengths they share.
If you bought a 24-70 that wasn't really sharp at F2.8 and you had to stop it down to F4 to find the quality you're looking for, what is the real point of having it? You probably could have gone with the 24-105 and gained IS plus a longer focal range. (in a much lighter setup as well)
Get the 24-70 for the F2.8. Get it for the bokeh. Love it. Otherwise, there is great value in the 24-105.