For my money, I'd probably put '2001' at the top for sci-fi. I guess Kubrick is either a guy that you really get, or you really don't........and I guess I happen to fall in the crowd that "get" him because the likes of '2001,' 'The Shining,' 'A Clockwork Orange' and 'Eyes Wide Shut' are some of the most beautifully shot, hypnotizing movies I've ever seen, featuring smart stories and boasting unbelievable performances.
Scott's other sci-fi film that he made only like 3 years before this, 'Alien,' features a similar dark, gritty, detached tone.
And similarly, it's also considered one of the best sci-fi movies of all-time. Even voted top-10 sci-fi films by AFI.
Better than Camerons' 'Aliens' I think. Cameron loses the dark, gritty tone and thrilling suspense and instead creates a fairly campy, all-out action movie.