Don't know if it's the best, but one of the most disturbing (and downright scary) films I've ever seen is Henry: Portrait of a Serial Killer, a film based loosely on the crimes of Henry Lee Lucas.  I saw that. It was indeed disturbing. As far as the best I couldn't say. It would change every day. Right now it would be a tie between "The Lost" and "Nosferatu".
"When the snows fall and the white winds blow, the lone wolf dies but the pack survives."
Winter is Coming
Now this is the Law of the Jungle—as old and as true as the sky; And the wolf that shall keep it may prosper, but the wolf that shall break it must die.
As the creeper that girdles the tree-trunk, the Law runneth forward and back; For the strength of the Pack is the Wolf, and the strength of the Wolf is the Pack.
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