Need some help deciding between these two lenses for my next purchase. I have a 5D2 and the wife has a 40D. This will mostly be used on the 40D as I have a 70-200 f2.8 IS II on my 5D2. The purpose of the lens is mainly for travel. Right now she has a kit lens (17-85) and we want to upgrade. The Tamron is a little pricier, but not enough to influence my decision. I've watched and read a lot of great reviews for both. People rave that the 24-105 is one of the all time greats in Canon's line-up. Similarly, a lot of people talk about how great Tamron's 24-70 is with VC. The Tamron has the f2.8 advantage. Not sure how the two compare in IQ. Let me know which one you would choose and why.