My EOS R is open to a bit of experimentation!
The A7 III is certainly a power-house of a 4K camera but it does have one strange issue, which only occurs in full frame 4K mode.
A great feature few have really talked about so far is that the Panasonic GH5 will allow LUTs to be loaded onto the camera.
At NAB 2016, Sony announced the free version 2.0 firmware upgrade for the FS5 and the paid RAW update. This will enable 4K 60fps RAW and 1080/240fps RAW via 3G SDI to the Odyssey 7Q+ external recorder.
The Canon C300 Mark II appears to have a firmware bug. This will need a fix from Canon if the C300 Mark II is to be completely bullet-proof on a shoot.
Highlights burn to black in certain situations (as with car headlights or the sun).