I have a 7D body, with sigma 17-70, canon 70-200 f/2.8 IS II, and I recently replace sigma 17-70 with canon 24-105 IS. The 24-105 is for sure the lens if you can only carry 1 lens. It is a lot sharper than sigma 17-70. I was debating on 24-105 f/4 IS or 24-70 f/2.8 for a while. The new 24-70 II makes the old look bad, and the new one is way to expensive, and without IS. The 70-200 f/2.8 is so heavy, unless I know I will need to use f/2.8, I don't want to carry it.