Bdunbar79 and RMC33, from what I gather, the 24-70 Mk1, has better bokeh...and for portraiture, you don't always want ultimate sharpness. Not sure I see myself buying a used Mk1 when I go full frame, though. Also won't buy the Mk2. Since I don't do much portraiture, I probably stick with the 24-105 kit, and maybe get a Tokina 16-28 at some point. I feel the 24-105 is (or can be) sharper than the 24-70 Mk1...at least based on my cousin's RAW landscape files I've worked on (he has the 24-70 Mk1 on a 5D3)...and comparing them to my own files from renting the 24-105 with a 1 series body. The 24-105 has more CA in the periphery, though, and possibly a lot more barrel at the wide end...both easily correctable though.