I have the SP24-70VC and it is amazingly sharp, the VC (IS) is wonderful (at least 3 stops) and I highly recommend it. It is far superior to the 24-105, which I also have. I would sell the 24-105 and pick up a 70-200. The reviews for the Tamron are very good, though I have no experience with it. I do have the 70-200L f/4 IS and think this is one of the best affordable lenses on the planet. Hope this helps.