I would say the best OD/ID/SB player. Or with other words: the best defensive player by rating (how this rating is calculated is another question)
I think we established beyond doubt that this is not the case with your Haek examples (where he was not picked to be the mtm guy)? I can probably prove it as well with Ma Anhui in a scrimmage later on in the season, since the difference between him and the rest of the defensive options is very big.