And so, the two leaders of the Horde who manipulated this for their own purposes and who serve a great evil. Who do you think is more evil?
Who will win the battle (Gul'Dan in his red hulk form, the current Sylvanas)?
And so they would think about each other? I mean, they clearly would not love each other because Gul'Dan serves Sargeras and Sylvanas serves the Jailer, but perhaps they would have mutual respect and admiration for each other's ability to manipulate and foment war. Blizzard said that Sylvanas considered Garrosh to be an amateur, perhaps she would have had more respect for Gul'Dan.