[hanamizu]

My vote would be for “The Haunting”.

Although not a horror movie per se, The Thing from Another World (1951) really scared me when my parents thoughtfully took me to see it when I was five. Years later, it still gives me the chills.

[Inyo-Mono]

I too saw “The Thing from Another World” as a child in the 1950s and it scared the c#@p out of me. The Kurt Russell version, “The Thing,” years later was even scarier.

[mass55th]

"My vote would be for “The Haunting”.

That was my choice too. I saw it in the theater, black and white flick, and very intense for that time period.

[ApplegateRanch]

The Haunting..
“If it wasn’t you, then who was HOLDING MY HAND?!?

Saw The Thing From Another World about the same age you did.

A few years later...
The Quatermass Xperiment (a.k.a. The Creeping Unknown in the United States) in 1955