I stressed over which lens in this range to buy for a bit over a month. Ultimately I ordered the Tamron 28-75 yesterday. From all I have read, and all the pics I have seen, it just looked like the best fit for me. The 24-28 is probably more of a difference than the 60-75, but I find that I tend to shoot longer and the extra reach was really desired. Most of the wider stuff I noticed I was shooting tended to be landscape or big group shots, and those tended to be stopped down anyway, so I could use the kit lens to cover the stuff below 28. Also, I liked the colors a bit better on the Tamron, and in most of the backlit shots I saw (yes, sometimes you just need to take the shot with the sun behind your subject), the Tamron seemed to handle CA noticeably better. The only real advantage I saw to the Sigma was in build quality, and the Tamron is not flimsy. In the hundreds of posts I read, and the hundreds of pics I saw, a good copy of the Tamron (and most were good copies) were favorably compared to the Canon 24-70. Very few people even tried to compare the Sigma to the Canon.