There is one advantage of nvidia proprietary driver, you get support of new cards on day one, with amd/intel it takes few months to have drivers in good shape.
I'm pretty sure amdgpu has supported AMD's recent cards (from the past few years) before they hit the shelves. Same for intel. It's always fun seeing the commits adding support for chips that you can't buy yet. And I've bought some very bleeding edge hardware from both companies in the past few years, with good results OOTB on Linux.
