Probably Rosemary’s Baby or The Shining
The past 15 years have probably been the best time for horror ever though. It’s the genre that I feel has been most progressive and creative. Some really great horror movies and a lot of good ones.
Great ones like Hereditary, The Lighthouse, The Descent, Saw, Let the Right One In, Get Out, Us, The Witch, You’re Next, The Wailing
Good ones like Midsommar, Hush, Oculus, It Follows, Don’t Breathe, The Invitiation, Evil Dead remake, paranormal activity, dawn of the dead, Final Destination 1, The Strangers
And then you have ones that are well made, decent horror movies worth watching like ]The Conjuring 1 and 2, Sinister, Saw 2, Insidious series, It, A Quiet Place, Geralds game, Rec, Trick r Treat, Hostel etc
There are quite a few more as well
Which other period of 15 years or so in history has had this many good horror movies. Compare this to the amount of mediocrity in the decades after the 70s.