The films mentioned are among what I like to call "Hammer's neat little black-and-white psychological thrillers" - most are very well-done with excellent performances. I've just re-watched NIGHTMARE and PARANOIAC - indeed, a fine double-bill!
"In
my
case, self-absorption is
completely
justified."

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Ariane,
Your rankings are spot-on with mine. Scream of Fear is definitely the best of the trio, Nightmare comes in second, and Paranoiac a fairly distant third. Still, I like all three. So far Scream of Fear is my favorite Hammer film.

Hammer made a dozen of these movies. Here's a list:
http://letterboxd.com/davejay/list/hammer-house-of-psychos/

For me, Scream of Fear is one of Hammer's best, a true jewel with amazing black and white cinematography.
Then I'd place Nightmare, also a powerful thriller, then only Paranoiac - a good Hammer film noir but far from being as unique as Scream of Fear.
only my opinion, of course !

"Don't act, be !" (Kate Winslet)

There was also The Nanny, written by Sangster, directed by Holt, starring Bette Davis, although it's not quite similar enough to Scream of Fear and Nightmare to fit in as a 3-piece. I am going to see Paranoiac when the disc arrives from Netflix. In your opinion, where does it rank when comapred to the other 2 of your trilogy?