B&H Photo Video has posted a buying guide for currently Sony a9 and a7 series full frame mirrorless cameras. If you are planing to purchase a Sony full frame mirrorless camera, you’d better take a look at this buying guide here.
From B&H Photo Video:
The a9 and a7 II are placed at completely different prices and were released years apart from one another, and then the a7R II and a7S II are both specialized tools that are destined to falter somewhere in the feature set. All the cameras performed extremely well, and you really shouldn’t have any issues to worry about.