For me, it was always Optimus Prime from The Transformers movie.
Snape is the best part of the latter books. He’s well rounded, motivated, and a fully fleshed out character.
The rest of the world and half the people in it feel like cardboard shuddering in the breeze by that point.
The plot twist was that Snape wasn’t a traitor, and killed the dying Dumbledore to save Draco Malfoy from becoming a murderer.