Aliens, but I'm not a fan of straight-up horror, which rules out Alien for me. I've watched it up to the part where they find the eggs, if that counts, and I've read the novelization.
I was also exposed to the chestburster scene at age 5, which may explain a few things.
3 committed the unforgivable (for me) act of killing Newt and Hicks (and mostly-Bishop), and I'm still baffled by the "logic" of the opening, and Resurrection was just pretty bad overall, though it had moments of not-badness (the failed Ripleys was pleasantly disturbing).

3 committed the unforgivable (for me) act of killing Newt and Hicks (and mostly-Bishop), and I'm still baffled by the "logic" of the opening, and Resurrection was just pretty bad overall, though it had moments of not-badness (the failed Ripleys was pleasantly disturbing).