I shoot full frame and have owned both of these lenses, although had the 24-70 for longer than I've had the 24-105 so far. From what I've experienced so far with the 24-105, the IS can nearly make up for it being an f/4. A whole stop of exposure is gained from its largest aperture being f/2.8 on the 24-70, but it lacks Image Stabilization, and it's kept me happy knowing that I can bump my shutter up two thirds of a stop and turn on stabilization (usually leave it off because I'm with a tripod the majority of the time) and still have a very similar exposure, but with a deeper (just slightly) focus and slower shutter (which sometimes can be too slow for what it's being applied to).
The 24-70 would be better for you if you spent most of your shooting time at contracted events, such as wedding ceremonies and commercial work. I've used both lenses for reasons as this thread is titled. So, when lugging around a full frame body that's not a Leica, soooo something heavier than your standard aps-c type of prosumer, for the sake of functionality and usability, I say go for the 24-105 if you ever do invest in either of these lenses. The 24-70 II is out of most our budgets, I'd assume. If cost wasn't an issue, I'd recommend that based on the reviews I've seen about it sharpness stacked up to its predecessor and its weight as well. If you're going to carry around a DSLR with a daily driver, you may as well make your setup as light as possible with the most range without giving up image quality.. therefore 24-105>24-70. When i switched to Canon, and even before, I always drooled over the 24-70, but I'm happier with the 24-105 at the moment.