So Science Fiction has to be based on real science now? Did they change the rules?
Frankenstein is my favorite novel of all time, regardless of genre.
The Sherlock Holmes stories are 2nd on my list.
Flowers for Algernon is probably 3rd on my list.
After that, the Hitchhiker’s Guide series, On A Pale Horse (and others in the Incarnations series, but I think On A Pale Horse was by far the best of the series), and I Robot.
There’s a lot of SF in my top ten. Heck, there’s a lot of SF in my top 100. 
It depends on whose rules you’re playing by. Interesting discussions can be had (and have been, here and elsewhere) over the definition of “science fiction”; and some people argue, with some justification, that it matters that the word “science” is in the name of the genre.
I’m tempted to say that voyages to strange, imaginary places (as in The Odyssey or Gulliver’s Travels) are works of fantasy, not science fiction; and that, at least before the 20th century, the fact that those voyages involve travel through space rather than over the ocean doesn’t make them any more science fiction, since it was only in the 20th century that the idea of space travel was based on science and technology. But I haven’t convinced myself, and there are good arguments on both sides.
I feel more confident in asserting that Frankenstein is the earliest example of a particular type of science fiction. It is about science and scientists. And it is a realistic novel, in the sense that it is set in the real world, and once you grant the premise (that a scientist has discovered a way of creating life), everything else follows naturally.
CalMeacham:
Haven’t forgotten it - just don’t like it very much, and this thread is about our favorites.
That one is just terrible.
I was going to mention John Sladek, just because he’s one of the few SF authors I’d never heard of until last year. A friend gave me a copy of The Reproductive System and said “Here. My favorite book.” More absurdist social commentary than hard sci-fi. But hilarious – Kurt Vonnegut meets Douglas Adams.
I always thought that the idea was the inspration for Frankenstein was loosely based on an urban legend that Erasmus Darwin brought worms back to life using electricity, Not real science, but then again according to the current state of physics FTL should be impossible as well.
Here’s a little known but interesting example: The Blazing World.
Hardly real science, but you do have to pretend. I consider The Martian Chronicles as science fiction though the science involved is not much better than Frankenstein.
There are whole books on early proto-science fiction, with bunches of stuff that predate Frankenstein and are just as science-y. I just read it, so my memory’s fresh. There’s not an ounce of science in it. Frankenstein gathers some human parts together and undescribed magic happens. It’s like those books in which sex is indicated by some asterisks and people lighting a cigarette. Don’t believe me? Here’s the big scene, in its entirety.
I don’t know what my favorite might be, but I know that I used to argue that Dick’s The Man in the High Castle was the pinnacle of the field. I haven’t reread it in decades and I find almost all older stuff unreadable today. But it a great argument against people who think sf has to include spaceships.
And as someone who just read around 400 robot stories, 390 of which were pig-fodder, I need to recommend one of the ten which weren’t. The novella “Silently and Very Fast” by Catherynne M. Valente is a marvel, a rethinking of the entire subgenre of brains that become self-aware. The beginning’s a bit hard to get through, but it all comes together in the end.
Which leads me to wonder if A Princess of Mars is science fiction or fantasy. John Carter doesn’t get to Mars any more realistically than the travelers in the earlier works, but what he finds there is a bit more plausible given the science of the day. If he went by rocket, and everything else was the same, would it be more like science fiction?
I read Clarke’s A Fall of Moondust about once a year.
I read most Hugo and Nebula nominees, and I enjoy them for the most part. Since most folks are naming classics, I’ll name the best one I’ve read in the past decade–and I’m limiting to the pleasures best given by hard science-fiction.
It’d be The Three Body Problem, a helluva novel that has enough jawdroppingly cool ideas in it to populate any three lesser novels. It’s well worth your read if you enjoy traditional science fiction.
I’m going to say my favourite sci fi novel is Slaughterhouse 5, though I don’t really categorise it as sci fi in my head. It has aliens and time travel, so it has to count. But it just doesn’t feel like it is.
Still, it’s my answer. I’m sticking to it.
The Moon is a Harsh Mistress
I’m reading this thread because I know essentially nothing about the genre. I don’t understand what belongs and what doesn’t, but I do have sort of an idea that seems to resemble something that’s lurking in this thread: the relationship of the story’s characters with the story’s science. It feels to me as if - for a rough example - if the characters ride somewhere in a spacecraft but we don’t see them interact with or refer to the science behind that craft, then they might as well be riding in a K-car.
Similar to if there was a sports movie where all the action took place inside the locker room, or an action movie that only showed a narrator sitting in a rocking chair explaining what happened.
The Left Hand of Darkness.
Player of Games by Banks is my favourite (today).
So hard to choose, but I think for me it’s a tie between two Heinlein novels, Double Star, or The Moon is a Harch Mistress.
For short stories it would be a tie between Heinlein’s The Man Who Traveled in Elephants" or Spider Robinson’s True Minds.
Which is precisely the issue when you separate science fiction from fantasy. I argue they are essentially the same, except that the fantastic events in SF have a “scientific” cause (and thee quotes are deliberate).
Samuel R. Delany has pointed out it’s impossible to come up with a definition that includes all cases that the definer considers science fiction but excludes all cases that the definer does not.
I would certainly argue that at least some parts of Gulliver’s Travels are science fiction. Lilliput and Brobdingnag are pure fantasy, to be sure, but Laputa is a society distinguished from ours by their significantly greater level of technological advancement. What’s more SF than visiting a land of high technology? He even meets my personal criterion of “hard science fiction”, that is, that the author needed to do calculations to write the book: He tells of the Laputan scientists having discovered moons of Mars (then unknown to real science), and correctly uses Kepler’s Third Law to describe their motions.
Isn’t that the one that has robots powered by generators in their own joints, so they can keep running indefinitely as long as they keep moving? If you’re going to stick a perpetual motion machine into a science fiction story, you had darned well better make that machine the main focus of the story, and explore the implications in considerable depth, if you expect me to take the story seriously.