Science fiction:
1984, George Orwell
Slaughterhouse Five, Kurt Vonnegut
The House of the Scorpion, Nancy Farmer
Horror:
Frankenstein, Mary Shelley
Fantasy:
Harry Potter series, J.K. Rowling
Gemma Doyle trilogy, Libba Bray
His Dark Materials series, Phillip Pullman
Song of the Lioness series, Tamora Pierce
Inkheart trilogy, Cornelia Funke
It seems I have multiple favorites in science fiction and fantasy. I hope that's fine.