There are various lists ranking the best sci-fi movies and shows of all time, with some outlets providing their own rankings and others citing the opinions of critics like Roger Ebert or users of platforms like Letterboxd. The rankings appear to differ across outlets, with some focusing on specific sub-genres like sci-fi adventure or thriller movies. The lists seem to cover a range of time periods, including all-time rankings and those focused on specific decades, such as the 2010s.