As I kid, my favourites were:
Matilda - Roald Dahl
The Witches - Roald Dahl
Charlotte's Web - E. B White
Don't Be Silly, Mr Twiddle - Enid Blyton
The Worst Witch - Jill Murphy
And I obviously love the Harry Potter books. They weren't published until I was about 12, but I didn't read them until I was 17. I'm gutted!
If I'm honest, I really enjoy YA fantasy fiction, in a lot of cases, more than Adult. My partner always says that Potter is for kids, but the truth is it is a fantastic story, and so often YA book are just great stories. Who really cares what age group it's marketed for?