Sorry, too tough of a question. I think I'd have a better shot at picking five nonfiction books... Even if the dimensions were clearly defined, picking the top SF would be really tough. And should fantasy be included in the consideration? Two examples did pop into mind in response to your question, though I don't think I could claim "top" status for either. I thought the style of Stand on Zanzibar was quite impressive, but perhaps it was merely one of the first multi-threaded books I read. In the humor category When Harlie was One comes to mind, but maybe that's AI overhang? Asimov wrote some great stuff and I was big into Heinlein for a while, but I think I grew out of his stuff. I already mentioned Banks as a more recent author whose SF work I mostly liked. Seems like I've mostly stopped reading SF now... Only four books last year out of more than a hundred... I see one from Vernor Vinge, another excellent author, a Frederich Pohl, and two from newbies Becky Chambers and Edward Ashton. Also nearing the end of The Best American Science Fiction and Fantasy 2022 without much liking any of it.