Sony, Canon and Nikon seem to be leading the megapixel race at the moment. The D800 series while not always as high resolution as the Canon 5D, leads in dynamic range when considering the high resolution options. The Sony mirrorless gives you a slightly small body option.
Its hard to think about Medium Format when you have bodies as capable as those.
My digital work is now all Nikon D800 and Leica M10, 35mm full frame 36 MP and 24 MP. I generally shoot the Medium Format and Large Format just for fun. When looking at cost and resolution 35mm seems to be winning the war, unless you need a 100 or 200 MP Medium Format monster.