It depends on genders sometimes. Because I'm a girl, and personally I love romance books, but I also love thriller and horror stories.
Maybe it's different from a boy's view, but I'd imagine they're more into things like horror.
within that catorgory, id say sci-fi, or for teenagers probably books about wizards or vampires. .> harry potter. i hate those books haha XD
Probably romance although fantasy is strong competition
From the people I know I would say sci-fi/fantasy.
Romance, definitely, or Fantastical Romance.
DEFIANTLY NOT NON-FICTION.