Baine's refusal to kill Magatha for killing his father. He gives her a "The Reason You Suck" Speech, and exiles her, without the quarter of her followers who chose to join him, clearly showing that while a part of him wants revenge, he has managed to overcome this desire for the good of his people.
Garrosh's reply to Magatha's request for support demonstrates that he was a much better writer than a Warchief.
"You are on your own, Magatha, as friendless and disliked as you have ever been. Perhaps more. Enjoy your loneliness."