Sony a7R III
The a7R III doesn't offer increased resolution when compared with its predecessor, but that doesn't mean it's not a serious upgrade. It takes a sensor that's already proven to deliver excellent performance and ekes a bit more dyanmic range out of it, while other upgrades are more palpable.
Proven 42MP full-frame sensor; Improved processor and autofocus system; 10fps image capture with tracking; Silent shooting option; Tilting touch LCD; Dual card slots; Larger battery than a7R II
Only one card slot supports UHS-II speeds; No built-in flash; No in-camera time-lapse support; Can't start video until image buffer is cleared; Dense menu system