In your case you might want to look at the 24-70 f/4 IS. It has the sharpness of the 24-70 II, with better IS than the 24-105. But, it is overpriced at the moment for sure as its now a 5diii kit lens. Probably will be in the $1000 range in 3-6 months.
The 24-70 f/4 IS, is not as sharp as the 24-70 f/2.8 II. Similar sharpness to the 24-105L according to the TDP comparisons (link below). The 24-70 f/4 is sharper with less distortion at 24mm and 70mm, but the 24-105 is better at 35mm and 50mm.
I believe some other CR members have had better luck with their copies of the 24-70 f/4.0 however.
The 24-70 f/4 IS does have the advantage of being somewhat smaller than the 24-105 and has near macro capability, but until its street price comes down considerably, I can't see it being worth the money compared with the 24-105L. If the prices does drop to $1K, it would probably be a decent value.
I dunno, I've been looking at a lot of real-world A/B comparisons of photos and while the 24-105 is just as sharp in the center, it seems to be less sharp in the corners with increased CA. Just what I have observed. And technically the IS is inferior to the IS in the 24-70 f/4...
I think the extra range of the 24-105 is pretty cool to have though, especially if you have an a crop in addition to your FF. Ideally, if you were to have two it might be neat to have a 24-70 f/2.8 II and a 24-105 IS. But if you just picked one and wanted the best IQ in the smallest package, I'd say to go for the 24-70 f/4 IS.