The first sci-fi novel I ever read was Dick's "Our Friends from Frolix 8", which probably wrecked me for life, btw (I was 12 or 13). That was from the local library, and the prior week I'd read the Lewis Carroll novels. Around that same time I read "The Hobbit" (having never heard of it before, it was recommended by a friend who'd found it in the school library) then borrowed LOTR from my sister. From that point until my college years, I probably read it about six times, but got to the point that I skipped parts, like the Old Forest/Barrow Downs. The parts I used to skip I skipped again when I re-read it for the first time in decades, just before the first movie came out. They skip the same parts.
I wound up buying a number of the Conan paperback when Lancer was publishing the revived, adapted, or whole-cloth new ones. A bunch of those fell out of copyright (author R.E. Howard killed himself so long ago, intestate I think) and can be found online. Some of those could make good TV series episodes, IMHO, but they aren't much to read at this point. In high school I was off novels for the most part, read some Ray Bradbury and Kurt Vonnegut.
I gave up on the sci-fi genre in my early 20s after Asimov's "Foundation" trilogy and a bunch of collections of short stories (Theodore Sturgeon, some of the Thieves' World stuff, the World of Tiers, and from my sister's collection some A.E. Van Vogt after the Asimov). Another novel I'd group in there was the utterly tasteless "Aton", author I don't remember. In college I borrowed some other stuff from fellow students, the only one I remember offhand was "Hadon of Ancient Opar".
Then in my mid-20s I borrowed some paperbacks from my sister (again), Larry Niven's "Ringworld", and "Ringworld Engineers", and somewhere in that general time frame his collab with Jerry Pournelle, "Lucifer's Hammer". I wound up buying "Venus on the Half Shell" at a big paperback exchange in SF, read the whole thing, swapped it back for some other crap, didn't finish the other crap, sold it back before I went home.
Thanks to Tolkien, I got sidetracked into the sword and sorcery stuff, including Conan, but also tried the Gormenghast Trilogy (Tolkien's popularity meant that trilogy marketing was everywhere), and E.R. Eddison's fake trilogy. The paperback of his "A Fish Dinner in Memison" is my favorite cover art for any book, ever, btw.
The only sci-fi I've read since my 20s has been some short stories (more Dick) and by recommendation of a FReeper, Hogan's "Inherit the Stars". By the end of his life, Hogan was deep off into Holocaust denial, which may explain why his Giants series (I the S being the first of those) never got made into movies AFAIK.
Anyway, top three, first one the only one I'd read again, the others odd, obscure maybe, nostalgic:Do Androids Dream of Electric Sheep? -- Philip K. Dick
The Last Astronaut -- Pel Torro
Daybreak 2250 AD -- Andre Norton (originally published as "Star Man's Son", and republications have often alternated the titles)
I wouldn’t trade any of these into my list of three, but I forgot to mention the Ursula K. LeGuin sword and sorcery stuff, which I’m sure influenced some of the Star Trek scripts about the Klingons (just a hunch, really).
https://en.wikipedia.org/wiki/Ursula_K._Le_Guin_bibliography
Other than the implausibility inherent in any paranormal crap that wind up on sci-fi (which is, after all, a branch of the horror genre), I’ve always thought this one pushed many of the right buttons, and one really wrong one.
https://freeread.com.au/@RGLibrary/RobertEHoward/REH-Conan/TheHallOfTheDead.txt