I liked Foundation and just about all the other pre-1970 Sci-fi books that will be mentioned in this thread, but the Sci-fi book that changed my life was the 1909 book “The Machine Stops” by E. M. Forster, which I read as a boy.
“https://manybooks.net/book/137318/read#epubcfi(/6/6[html3]!/4/40/1:0)
I firmly believe that "We All Died At Breakaway Station" is the best combat science-fiction novel ever written.
The Lensman series by EE “doc” Smith.
The Late, Great Planet Earth
Book Of Mormon
Job: A Comedy of Justice — Heinlein
Stranger In A Strange Land by Robert Heinlen.
The Talisman by Stephen King.
All Good
Bkmk
Dune
Foundation
Stranger in a Strange Land
Lords of Light, A Canticle for Leibowitz, A Scanner Darkly
1. Foundation Trilogy by Isaac Asimov
2. I, Robot by Isaac Asimov
3. Noumenon by Marina J. Lostetter
Mote in God’s Eye
While I enjoyed most of the books that were mentioned previously, I will add Hyperion by Dan Simmons.
If I go by what I have reread the most, even then it is tough to come up with a top three. But. . .
Heinlein Moon is a Harsh Mistress (although Friday gets about as many rereads).
Card Ender’s Game
Niven Mote in God’s Eye
If you incude “series” -
Asimov Foundation
Heinlein Future History
Niven Known Space
Does Adams Hitchhiker count as SciFi?
And if you include Hitchhiker, do you also include Harrison’s Stainless Steel Rat?
As for most recent reread in order -
The Martian
Card Shadow of the Giant
Card Shadow Puppets
Card Shadow of the Hegemon
Card Ender’s Shadow
Card Ender’s Game
Niven Smoke Ring
Niven Intefral Trees
Niven Destiny’s Road
Niven Gripping Hand
Niven Mote
Heinlein Friday
I think that’s it for this year.
Time enough for love
The moon is a harsh mistress
Stranger in a strange land
1984
George Orwell’s “1984” would be at the top....but its now moved to Non-Fiction....
Dreams From My Father
-Barrack Obama
A Canticle for Leibovitz
TheFoundation series
Ring World Engineers
Impossible to say.
one that sticks out in my mind is The Boat of a Million Years.—1989 by Poul Anderson. Past sci fi golden age and I could probably think of a few better ones if I studied it for a while.
still, it was good.