Back to topic, I agree with
@Barbara Fan and prefer "The Omen" over "The Exorcist", maybe because the latter has been spoofed so often (even by its main star Linda Blair) that I can´t take it seriously anymore. Though I did like the prequel they did more recently (director´s cut please...).
"Is that you, Lindsay...?"
"The Omen" was way more interesting and prestigious in every way, from the whole cast (with all respect due to the great work of Burstyn, von Sydow and J. Cobb in "TE"...) to the soundtrack and from the scary scenes to the fact that, to me, its 2 first sequels were quite more appealing than what came after the first "Exorcist" (which anyway attracted a lot of excellent actors to it, like Richard Burton, Louise Fletcher, George C. Scott and even a cameo of then-unknown Samuel L. Jackson in Part 3).
"It´s him, oh yeah..."
All in all, I´d dare to say that it was a sum of all factors what made these movies and this genre resurrect (though it was never dead, ahem...): good acting, scary scenes you loved to watch in a theater with friends or dates, chilling atmosphere, amazing music and direction...And yes, I think "Rosemary´s Baby" already had all that, and maybe it was the one that led the producers to follow the trend, but there are many others from the 60´s that also were very good (including the awfully titled genre of "horror hag movies" which I (and Miss Piggy too) prefer to call "grand guignol"...).
Moi has just found out that "Baby Jane" homaged "Psycho" itself!!!!!
From "The Innocents" to the Davis-Crawford vehicles (together and separately), to the gorgeous-looking B/W Hammer films to "The Haunting", all of them were scary as hell and, what moviemakers did in the 70´s was trying to make them more realistic and gory. I´d take anyone from this decade over the self-parodies that were made in the 80´s that everybody considers as "horror movies"...
Oh and I still think that Elizabeth Gilles is the reincarnation of Chucky´s Bride...