How you decide if a horror movie is one of your favorite?

I was thinking lately my top favorite horror movies (lake mungo, noroi and scream 1)

Lake mungo and Noroi scares the shit out of me but not scream 1. I love scream 1 because of the plot and characters.

How you decide if you love a horror movie? What it makes your favorite? Plot and characters? It's disturbing? etc