For me it has to be the Sept getting blown up. Honestly Cersei is my favorite character, I hope she wins in the end even though I doubt it's going to happen. She's just a fantastic character. That whole scene was a masterpiece with all the moving parts and the music, such satisfaction watching those nutjobs getting blown up too. If only Joffrey hadn't died, he'd have dealt with those creeps right away!
Favorite kill/death in the whole series for me was the knife in the face x3 from that episode with the Hound and Arya in the tavern (the infamous chicken scene!). When he's wrestling with that guy, turns the guy's own knife on him, then pushes his head face first into the knife three times was just nutso brutal.
CLEGANBOWL 2019, we gotta see it!!
6:50 for a refresher!