One Piece follows a systematic and fairly redundant format. Straw hats enter an island, straw hats get separated, straw hats defeat enemies of island from weakest to strongest, Luffy beats big boss of the island.... The end. The villains all fall into similar categories of oppressive overlord of an island that the straw hats need to save. The pacing is as slow as can be, however, the world itself is imaginative and eventful.
Characters in One Piece rarely develop. They mostly take on new roles they wouldn't have before, while maintaining the same characteristics. What I mean is most characters are already developed to begin with. Some characters like Zoro are development fiends. They change fluidly with the story, but that's a rarity in all honesty. I mean, Luffy is legitimately the same dude he was in chapter 1. No real change. The only development opportunity was when he lost his teammates, but that was all forgotten when they got together.
Overall, Naruto wins in both departments just for being different most of the time. The overall plot of One Piece should triumph in the end, though. I think Oda is really getting into his groove now.