I do not really like or read science fiction. I do read and like a great deal of fantasy. What science fiction I do read is very unsciencey science fiction. Stuff like Edgar Rice Burroughs' Mars series which are really nothing more than interplantary fantasy swashbucklers. Errol Flynn in space.
But they are not my favourite fantasy. As far as Burroughs go, Tarzan is a much greater fantasy icon. I also like the dark, moody poetry of Robert E. Howard, creator of Kull, Conan, and his best creation Solomon Kane. Conan Doyle also had some interesting excursions into fantasy.
But my favourite fantasy of all time is SHE by H. Rider Haggard. I have about thirty different variants of the novel (including two firsts), which stirs deep, deep waters...as do most of Haggard's fantasies -- things like The World's Desire, Red Eve, Alan Quartermain, so many others...Haggard is my favourite writer, probably.
A. Merritt and his wonderfully florid prose I find quite evocative. Things like A FACE IN THE ABYSS; CREEP, SHADOW, DWELLERS IN THE MIRAGE...they're like poetic fevre dreams.
I'm a big, big fan of English writer, Terry Pratchett, creator of the hilarious Discworld series...witty and smart books.
Though I prefer his mysteries, Fredric Brown's dabblings into Sci-fi and fantasy are entertaining, as all his writing is...often very brief and witty.
Cornell Woolrich, also a mystery writer, also had some interestng forays into fantasy that embrace his compelling prose style.
I'm a sucker for Sax Rohmer and his Fu Manchu novels and his other thrillers of orientalism.
One of the most exquisite writers of fantasy I've ever read is the little-known Thomas Burnett Swann. Died early. His books use mythology as his tapestry. His prose style is gorgeously poetic and his tales are heartbreaking, powerful, moving, and simple. Titles like DAY OF THE MINOTAUR, MOONDUST, WILL O' THE WISP, WHERE IS THE BIRD OF FIRE...wonderful, wonderful stuff!
And then of course, there is my pal Harlan Ellison...whose works transcend confining labels like science fiction & fantasy.