The Thing
This has been and always will be the best horror movie ever made. I abso-fucking-lutely love the special effects, they look so disgusting and grotesque that they truly convey how terrifying and fucked up the whole situation is. I also love how the story pulls the who is good and who is bad card by making the Thing assimilate its victims and integrating back into the group as if nothing happened, you truly don't know in who to have trust. The setting also helps out, by being isolated in the arctic, there is no real escape for the researchers. The Thing truly is out of this world.