Short version: the Shah’s regime, odious as it was, killed a little over 3,000 people between the early ’60s and its fall in the late ’70s.
The mullahs have killed unknown but vastly greater numbers, by execution, incompetent defense during the Iran-Iraq war, and generalized misrule — many times the Shah’s entire toll, each year. The grand total may reach into seven figures.
Ironically, by suppressing the relatively timid elements of his opposition, the Shah all but guaranteed that he would be succeeded by the most unhesitating killers among them. See Daughter of Persia for a terrifying account of the revolution (there is also a website for the author, Sattareh Farman Farmaian).