Which horror movie that you have seen be it old or new was so great that you gave it a perfect 10 out of 10 score? Personally I would say that The Ring fits that bill, same for The Conjuring. Both movies are very much perfect from every aspect: acting, soundtrack, story, atmosphere and cinematography, pacing, etc. They are also incredibly rewatchable and have nice little things for you to discover on subsequent viewings.
Said it before and I'll say it again: being a genre fan is tough. Also don't give out many 1s or 10s, and in horror there are only two of the latter and neither are likely to be a surprise: The Exorcist (1973) and The Thing (1982).
sharePsycho (1960)
The Exorcist (1973)
The Texas Chainsaw Massacre (1974)
Halloween (1978)
The Shining (1980)
The Thing (1982)
Fright Night (1985)
Return of the Living Dead (1985)
Evil Dead 2 (1987)
Damn some of you boys are stingy. Show some love!
The Innocents (1961)
The Birds (1963)
The Living Dead At Manchester Morgue (1974)
The Texas Chain Saw Massacre (1974)
Black Christmas (1974)
Suspiria (1977)
Halloween (1978)
Alien (1979)
Zombie (1979)
The Thing (1982)
Poltergeist (1982)
Tenebrae (1982)
Friday the 13th Part IV: The Final Chapter (1984)
Lifeforce (1985)
The Fly (1986)
A Nightmare on Elm Street 3: Dream Warriors (1987)
The Vanishing (1988)
Scream (1996)
Jeepers Creepers (2001)
The Ring (2002)
Freddy vs Jason (2003)
The Texas Chainsaw Massacre (2003)
The Texas Chainsaw Massacre: The Beginning (2006)
Final Destination 3 (2006)
[Rec] (2007)
The House of the Devil (2009)
The Thing (2011)
Sinister (2012)
Evil Dead (2013)
Hansel & Gretel: Witch Hunters (2013)
It Follows (2014)
The Night House (2020)