The main ones I'd put forward are Peter Pan himself, then Wendy Darling, and Captain Hook. But the trick is, J.M. Barrie's 'Peter and Wendy' (which I assume is the 'Neverland' book you mean) treats its characters less like heroes and villains and more like pieces of a strange, sad fairy tale. Peter is the heart—utterly selfish, forgetful, wild, and yet you can't help being drawn to his freedom. He's a fantastic character because he's genuinely kind of a brat, not just a noble hero.
Wendy is the anchor, the one who tries to bring a semblance of a mother and stories into that chaotic world. I've always felt a bit sorry for her; she's shouldering all this responsibility while being utterly enchanted by a boy who will never grow up with her. Then there's Hook, who is almost a tragic figure beneath the pantomime villainy—a gentleman pirate plagued by a crocodile and his own obsessions. The Lost Boys, Tinker Bell, and even the ticking crocodile feel like essential parts of the main cast, each adding a specific flavor to Neverland's logic.
The dynamic between these three—Peter's eternal childhood, Wendy's budding maturity, and Hook's decayed adulthood—really forms the book's core. It’ s less about good versus evil and more about different ways of being in the world, all clashing on an island where time works differently.