If it's 5-on-5, I would trust Kovacevic, now. If it's a power play, then I am fine with Barron, but he has more defensive lapses/decision making gaffes than any other Habs defenceman this season.
I also think Kovacevic would be fine short-handed with Matheson; he makes better decisions in his defensive zone than the other two. Harris is not fully developed in his defensive game yet, and in my opinion could benefit from some time in the AHL.