Can't decide: Naruto has so little room to grow because if I don't get a good ability, I'm fodder. Now, in One Piece, even if I don't eat a Devil Fruit, I can still be strong (Zoro), and in Fairy Tail everyone only has one magic, and depending on how good you are with your specific magic, you could be the strongest or the weakest (it doesn't matter what you have, but how you use it).
Because I know so little about OP, I'm going with FT.