Upload & Sell: Off
I own the Sigma (after two horrible experiences with the older finish ones), and have near access to two copies of the 1.8G. My selection would be based upon what my surrounding lenses do. The Sigma is more of a wide open sort of lens that has poor sharpness on FF corners, and the 1.8G is a lot more consistent throughout the frame.
If I had something else that's really good across the frame (e.g. 85 1.8G), I'd rather have the Sigma so that I have different lenses of not only focal length, but characteristics and limitations.
If I had something else, say a 85 1.4D that's got a reputable signature but isn't so good in the corners, maybe I'd pick up the 1.8G so that I'd have at least one lens that can provide edge to edge sharpness should a situation call for it (and the difference between the focal lengths isn't so great that I can't achieve similar framing).
as far as focusing, I'd say they're close enough that I wouldn't sway one way over the other. As others have reported, I didn't have that great of a time with the 1.4G's AF.
In my case, I have a 60 2.8G which serves as my staple, consistent lens, so I've kept the more exotic sigma with its imperfections.