A very difficult one. I spent a lot of time debating the same question.


I've had the 5DII for about 6 months now and the 24-70 for nearly a year, and on FF it's often not long enough. I do sometimes find myself swapping to the 70-200 for just that extra bit of reach, and on one or two occasions I've wanted to be able to zoom between 50 and 100mm easily. In these situations it's a hard choice between risking ending up with the wrong lens on or being caught mid-change.


That said, I daresay I'd miss the wide aperture of my lens if I'd gone for the 24-105. I asked lots of people the same question on several different forums and the concensus seemed to be that the 24-70 was better - someone made the interesting point that many who have the 24-105 wish they have the 24-70 but few who have the 24-70 wish they chose the 24-105. Whether or not that's true I'm not sure but it matched what I've read on various forums.


I think that if you intend on shooting even slow moving objects - ie people - in poor light without flash then go for the 70. If you think that anything you'd be shooting without flash will be stationary (so you can let the IS do the work) then go for the 105.