And why? Who do you think is the most neutral? Who is able to calm down the players and takes the best decisions (according to you)?

I think you have to respect the northern/southern hemisphere divide (for lack of a better word) in rugby world and name one from each. NH Nigel Owens SH Steve Walsh Those two would certainly have to be on anyone's short list. I know Walsh has some question marks on his record from earlier in his career, but seems to have settled down over the last few years.