Thanks for the inputs. I read the strengths on the net. Was hoping to get answers what sides of the cameras they find better from real world users.
As a Canon/Sony user I can't say how either or Canon lens with Sony camera compares to the Nikon, since I don't use the Nikon.
Because the Nikon shares the Sony sensor with some software differences, you are asking a question few can answer. Obviously the Nikon Camera is an excellent device and works well with Nikon glass and the other lens companies that have Nikon mounts.
Sony temporarily provides Canon users with a 36 MP sensor though an adapter. The Sony A7S has fewer MP but provides a silent shutter capability and a really high ISO, good for street and theater photography. While some adapters do allow for Canon lenses to be controlled by the Sony cameras. It's great to have all the exif data, too. What is not so great is that the focus is often slow and clunky to the point that it is often easier to just focus manually. I've found that putting on manual lenses with a non-reading adapter can be very useful, but I'm from pre-AF days and used to the procedure.
I knew before I went on the Sony path that I would have to make adjustments to accommodate the inherent weaknesses of the Sony system. The cameras, as others are learning, are not as durable or sturdy as either Canon or Nikon make their amateur bodies. Light leaks and loss of communication as the body and lens mounts flex under the weight of bigger lenses are beginning to pop up in lists of complaints.
The result is that, with careful handling, one can get good large print images of static subjects with the use of Canon lenses on the A7R; and one can get images practically in the dark with fast manual lenses on the A7S. For the time being, that is good enough.
Street artist with 7S, landscape with 7R, both with Voigtlander 35mm f1.2