For fantasy, and overall, I'm going to go for the various Tolkien Middle Earth works, mainly on the basis that I don't think any other modern work better and more consistently walks the line of of being functional and satisfying as popular entertainment while simultaneously feeling like it has real literary weight. Maybe you can think of a work that achieves the same, but Lord of the Rings was the bestselling novel of the 20th century, and whatever you're thinking of probably can't compare with that impact wise. And practically the whole fantasy genre exists to some degree in Middle Earth's shadow (if in many case's only in the sense that they employ world-building and Tolkien is far and away the most influential worldbuilder there ever was). Adaptations have been a mixed bag, but that shouldn't be held against the underlying work, and some of the adaptions have been impressive achievements in their own right.
But seriously, page three of this thread and Star Wars has only been mentioned (dismissively) once? Has the galaxy far, far away fallen so low? Look, prequels, Disney Star Wars, one or another lame novel from the 90s, an infamous holiday special... these things shouldn't matter. The original trilogy has more iconic things per minute than anything else ever committed to film except maybe Casablanca, to an extent that it's hard to really appreciate and easy to take for granted. Those movies are an achievement unto themselves, and I just don't think anything else Sci-Fi is really comparable. Whatever Star Wars media has come since is just a feather in the franchise's cap when its good, and when it is bad... well that should be insignificant compared to the power of the Force.
If Star Wars' star has fallen so far for you to not even be worth discussing I understand, but beware... it was a very different story at the franchise's reputational height (before the dark times... before the Phantom Menace), and whatever franchise you're going to bat for may yet suffer some variation of the same fate.