I think it has to be Mason. The problem has been a combination of both Mason and the D. You are playing the defending champs, I don't think now is the time to not show confidence in your starting goalie.
Mason is obviously the #1 but with Ellis showing that he is capable of winning a few games, I think Trotz should maximize this run and keep him in net until he falters. That way, Mason can have some time to work out some of the problems he's having. It's great that we have a capable backup that could stand in while our starter struggles. Mase will get going, just needs this wakeup call to light a fire under him.