I vote
Apollo 13 because the attention to realistic technology was about as good as Hollywood ever gets it. Just as important (because it is a movie) are the high production values -- even though everyone knows how the story turns out, the writing, performances and camera work generate tension and drama.
Apollo 13 is the only space exploration movie that gets weightlessness looking real... because it is real! Many of those scenes were filmed in NASA'a own zero-g aircraft, the infamous "Vomit Comet." That attention to accurate detail carries on down to the smallest things. At one moment, Gene Krantz is snuffing out a cigarette (everyone is smoking in 1970, naturally) and he is using a "bean bag" type ash tray. I remember those from the early 70s. Groovey, man!
Since it hasn't been mentioned yet, I would like to put in a commendation for
Deep Impact. (I confess, my favorable impression is influenced by my crush on Tea Leoni

) I also improved the film, on first viewing it, by arriving late at the theater, thus accidently "editing" the story to begin
in medias res. The audience knows the film is about a comet hitting the Earth, so the opening scenes of the comet's discovery aren't really necessary. The movie I saw began with the scene in the newsroom, where Tea Leoni, suffering junior correspondent, is tossed a crummy exploitation story about a Cabinet secretary's sex scandal. She works some connections and thinks she is onto some bimbo named Ellie. Accidental observations, odd happenings, over-zealous cops and dogged research brings her to the horrifying realization that "Ellie" is an acronym for ELE, Extinction Level Event, and the government is trying to keep a lid on the story until they work out a plan. The story is largely a character-driven "chick flick" which makes it unusual and internesting for science fiction.