Has to be
Florinda Bolkan.
Her ability to play women who have cracked up beyond belief, yet still remain a strong and unflagging character is magical. And she has a weird beauty, not obvious and certainly not in keeping with the busty blonds/redhead/brunettess of the 70s that were more common. Bolkan is otherworldly and dare I say Amazonian, not in the geographical sense of the word, although she does hail from Brazil.
Plus any actress who's been in the two best films Fulci ever made...
Top films:
Flavia The Heretic Le Orme aka. Footprints Lizard In A Woman's Skin Don't Torture A Duckling