If you have no budget issues, the 24-70 II would be hard to beat. Then lens is cracking sharp, benefits from whatever magic Canon has been applying to their AF systems over the last three years, and also has reasonable distortion, CA and vignette.
Another lens that gets a lot of love and which is a lot cheaper is the Tamron 24-70/2.8. You get a fast f/2.8 lens with IS for about $1000. I have no experience with this lens.
And then there is the 24-105L. I've owned my personal 24-105 since I got it with a 5D (classic) kit in 2007. My lens is quite sharp and I love it for what it can do, the handy range, the IS, and the weight / size. These days you can find used or broke-out kit 24-105 lenses for a song.
Here is my only real caveat on the 24-105, and one that probably won't bother you much. On the wide end of the range (24mm to 28mm) the lens has very strong barrel distortion and very strong vignette (on FF) that doesn't clear up until f/11 or so. That kind of performance might make a FF camera landscape photographer give this one a pass. For a 1.6X portrait photographer, it is no big deal.