I voted for "Halloween" (the original, of course) as number 1, because at the time in the 70's, I was doing a lot of babysitting and was kind of a bookworm and insecure about myself, and really identified with the main character Laurie. Also, I loved the creepy music, and the pervasive, ahead-of-its-time cinematography, such as the psychiatrist talking on the phone while the crazy escaped killer drives past in the station wagon, and the scene where all the lunatics are walking around the asylum in the darkness. I thought it was a very clever film, and as on every Halloween ever since, I've already got it cued up in my VCR to start at dusk when the kids come calling.
Voted for "Carrie" as number 2 because her eyes scared the crap out of me, and her mother was so anti-mother material. Plus I was in love with John Travolta / Vinny Barbarino at the time.
And "Amityville Horror" as number 3, once again because of the look of terror in Margot Kidder's eyes several times, and the scene with all the flies on the window just puts me into complete shivers every time.
I wish this poll allowed more than 3 choices, cause I've seen every scary movie ever, my parents put no reins whatsoever on my viewing pleasure as a kid in the 70's, and I could rate them from 1 to 30 if I had to. My next closest would be "Poltergeist", "The Exorcist", "The Omen", "Jaws". I would add several more that have been left out of the poll, let me think about it and get back.