I love Exorcist 3, and enjoy it more than I enjoy the original...however, I have to vote for Exorcist due to what I can only describe as a weird reason...(this might get long)...
I'm a Muslim.
What does this have to do with anything? When I first saw Exorcist (at 16 with no one else around) I felt that I had already seen it due to the massive hype and cultural references made to it over the decades: the levitating, the rotating head, the staris, etc.. What no one ever told me was how the film starts.
The first words you hear when The Exorcist starts is the adhan, the Muslim call to prayer.
I remember actually saying to myself "really?" I mean, for a movie with such strong Christian iconography, why a Muslim call to prayer? Why not Church bells? Was it just because it sounds foreign, and therefore, evil? Is it just another peg in the "Islam is a religion for brown humanoids"-board so common in pop culture?
However, and this is my interpretation, Islam is an Abrahamic religion, like Christianity. They share similar beliefs to a point, but are their own distinct religion. The common thread between these religions, is the belief in a monotheistic "God," and the translation for an adhan is roughly: God is great, God is great; there is no god, but God; praise be to God, the most beneficent the most merciful.
It surprises me that so many people don't acknowledge this detail in discussing The Exorcist. A movie about the mystery of faith and the presence of God and the Devil. We see plenty of the Devil, but where is God?
God's words can be heard right in the opening, but since the words are not familiar to 1973 White American audiences, then no one would actually hear them. So, maybe, God is there...but not there. God is capricious and plays with the characters and through the audience. And that to me is terrifying.