In various photo stores I tested the Tamron 24-70, the Canon 24-105 L and the Sigma 24-105 type on my EOS 70D. The result was more than clear. The Sigma delivered from the front mistress the sharpest results without any viewfinder based focus error. I was so impressed - and test results at full frame - that I do not long hesitated and struck.
After 500 photos at my past Hamburg-cities tour, I'm completely thrilled and confident. Wonderful contrasts, excellent sharpness. The AF sits. I had no disarming Committee. This was at the Canon 15-85 unfortunately the rule than the exception.
At last I can look through the viewfinder and me to be sure the end result is actually perfectly sharp and has no time for focus control waste on the camera display.
Color photo certify the AF performance of this lens on the 70D a good result. I find it visually but very good to perfect.
I did not have to seek in-camera focus correction!
The now missing 9 mm focal length wide-angle direction I want for APS-C indeed already, as I realized. But the problem dissolves at full frame almost on again. Besides, I'm still the Sigma 18-35 f1.8, with whom I again have more wide angle to APS-C. The 18-35 is incidentally also a perfect symbiosis with the 70D - tested by Color Photo and clearly confirmed by me. Top I have won with the 24-105 20 mm focal length, which I think is great. About all focal lengths, it delivers top results.
I am extremely pleased with the 24-105. Now I can make taking pictures with the 70D in standard situations turns into fun. The Bokeh Buttery soft feel and build quality are of type lenses from Sigma just a dream. Heavy the Kombi 70D with 24-105 is, but is wonderful in his hand. Concerns you have, however, that good filters with 82 mm diameter go neatly into the money. But it's worth it to me.
My clear recommendation for the 70D!