I've been using FF bodies for some time now. 24-105 I use as a general purpose lens. The limitation for me is the minimum aperture of f4. have tried the 24-70 but I found that the deciding factor between them is the IS. It allows me to handhold with longer shutter times than I could possibly obtain with the 24-70. A greater depth of field, but more shots are usable. If used for portraits, you will definitely have more than just the eyelashes of the subject in sharp focus which may, or may not, be what you prefer. By selecting locations where the subject can be further away from background objects you will be able to have enough blur to separate the subject, just not as much as a wider aperture.

In terms of IQ, neither is perfect and both of the lenses have their issues revealed in the ISO charts. In the real world there are many people using them to deliver high quality images. It just comes down to choosing amongst aperture, focal length range, and IS to best suit your own needs.