Of the two, I only have the 24-70 II, yet I often wish I had a little more reach. The range of the 24-105 seems ideal to me. In my film days, my trio was a 24, 50, and 100mm. But, the AF speed, accuracy, contrast and resolution of the of the 24-70 II are outstanding and I'm unlikely to give that up. About my only complaint with it is the size. It's just fat with the 82mm filter. :-)
All that said, I still think about picking up the 24-105 for certain occasions. But I'd prefer one with a 67mm filter to match the 70-200 f/4L IS.
Perhaps someday Canon will make a 24-105 f/2.8L IS, match the current IQ, and then we'll all know what to do.