This list is not in order of preference.
1/ Anne McCaffrey
I read ‘The White Dragon’ when I was nineteen, and have been a McCaffrey fan for ever after. I think the Pern books are great, but it is her ‘The Tower and the Hive’ books that I probably love the most.
2/ Ursula k. Le Guin
Every Le Guin book is something to treasure, but my favourites are her fantasy EarthSea series and her feminist Science Fiction classic The Left Hand of Darkness and her post-colonial/ecological Science Fiction classic The Word for World is Forest. Her short stories are gems.
3/ Jennifer Fallon
The Tide Lords is my favourite series, but it is hard to pick just one stand-out book in her bibliography. You always have fun when reading any of her books.
4/ Terry Pratchett
But he’s a fantasy author, you all protesting. May I direct you to the Long Earth series … written with Stephen Baxter.
5/ Vonda N McIntyre
If you haven’t read Dreamsnake or The Moon and the Sun, race out and read them right now, or I just can’t talk to you.
6/ Judith Tarr
I reread A Wind in Cairo at least once a year (it is a fantasy book). Tarr has had a long and prolific career, and writes both Science Fiction and fantasy.
7/ R A MacAvoy
Tea with the Black Dragon is one of my very favourite books of all time, but I love all her books. She is another author who can write both fantasy and Science Fiction books, with elegant ideas and enchanting prose.
8/ Diana Wynne Jones
You might be surprised at Diana Wynne Jones inclusion on this list. You can’t tell me that Howl’s Moving Castle, or A Tale of Time City, aren’t partly Science Fiction as well.
9/ China Tom Miéville
Okay … he has written books that can be considered part of the Steampunk oeuvre. However, most of his books aren’t in the Steampunk genre, but written in something he likes to call Weirdpunk. Most of his books defy genre definitions. And if that won’t entice you to read something of his, may I recommend Embassytown.
10/ Sean Williams
He is a New York Times bestseller. Go read the Twinmaker series, and thank me later.
And Lucky you! I’m making an extra recommendation: Elizabeth Ann Scarborough. Read Songs from the Seashell Archives Quintet and her Science Fiction collaborations with Anne McCaffrey.