Call it what it is.
Science fiction: that genre of literature spawned from the community of writers and readers based about the magazine Amazing Stories, first published in 1926. Often abbreviated to sf, but never to sci-fi.
Sci-fi is considered a pejorative by science fiction fans. Perhaps because it's used to put down sf works by some outside the genre. It might well be time we claimed the term back for ourselves.
It's not speculative fiction. All fiction, irrespective of genre, is essentially speculative. Calling something speculative fiction (or spec fic) is just a feeble attempt at disguising its true nature. Why be embarrassed about enjoying science fiction? You can call them pommes frites, but they're still bloody chips.