I see you did mention owning the Sigma 50 art. I saw the old Sigma 50mm EX for $350 last fall and impulsively bought it for a very fast (f/1.4) lens that could be used indoors as portrait lens. I found the 50mm and 85mm to be a big difference in focal length. How did you like the Sigma Art on your 70D?
The Sigma 50 1.4 Art was STUNNING. I did my first real job with it photographing 23 portraits for a law firm. It's really not possible to get better; as far as I could imagine. I compared the focal length with my 35 and the pictures were very similar. I definitely liked the 50 a bit better (a little sharper and a little more of that "professional" contrast, but not much), but the 35 is a bit more versatile so having both seemed expensive. I did my final portrait with the 35 and the results were nearly identical. The portraits with the 50 were just slightly more "natural" if that makes sense.
I would say that a 28mm would be a "better" general purpose focal length, but that's only 10 away from my 10-18 and 7 away from 35 and 35 is not bad for portraits as well so I figured that the 35 wins for more utility. Also, it's a 67mm lens just like the 10-18.