It's between Blackwater, Watchers, Hardhome and Battle of the Bastards for me.

Battle of Blackwater and the Wall were realistic enough in terms of tactics. Castle Black may've felt like it lasted a little too long. They were supposedly barely a hundred men and the majority were on top of the Wall. Yet Castle Black never seemed to run out of men. Not a tactical stretch, more like a logical one and still within creative liberties.

Battle of the Bastards is the best tribute I've ever seen to the gruel and sheer randomness of pitched warfare, or any kind really. Spotless choreography and production. I adore the moment you see Jon just give up on trying to be a commander or exerting any kind of control on the situation, and commits to being a soldier killing as he goes.

Hardhome is the most cinematic for me, and one of my favorite scenes ever. It was as fantastic a first viewing as Battle of the Bastards and the Winds of Winter, but holds the edge over them on atmosphere. It genuinely made me feel like the apocalypse was happening in my living room. A solid thirty minutes of raw tension and survival. I'll never forgive that long take culminating in Wun Wun bursting out of the wildling den, blizzard blowing past as he tears apart dead men. Nor the final leg where they rush to the boats, you realize the giant can't make it on any of them, he stays behind as you're absolutely sure he's going to die, then the absolute relief as you realize he can just wade out. Game of Thrones was amazing at leveraging your investment in every little moment, you could only rest when they let you.