One of my New Years resolutions was to change from a manual focus Nikon 85mm f1.4 to an auto focus 85mm f1.4 of some sort, as it is almost impossible to shoot a toddler with MF and get any keepers. The ultra thin depth of field and a moving object relegates this to a lesson in futility. So the lens got put in the drawer and not used, which is never a good sign.
The only real choices for an AF upgrade for me are the Nikon 85mm f1.4 AF-D or the Sigma 85mm f1.4. The last alternative is the very expensive Nikon 85mm f1.4 AF-S N, which is out of my league, even for a used one. Interestingly the Sigma the does not seem to be holding its value quite as well, and used examples are now trading in the $700 - $850 range, despite most reviews suggesting the performance between the two isn't too different, with a possible edge to the Sigma. The reviews for the Sigma generally are also good, and with the new 35mm f1.4 out, I was certainly keen if the right deal came up.
A few days ago I ended up purchasing the Sigma. Even at f1.4, the contrast and centre sharpness is really good, and the AF reasonably fast. Enough to ensure a good number of keepers to publish. Sure the corner sharpness isn't as good, but Im not worried as usually I am just looking at a dreamy bokeh instead!