One Piece lends itself to a more complex and well-written story. The advantage it has is that they can focus on whoever they want to on each island and have everybody else just support whoever is the focus. Be it Nami in Arlong Park, Chopper in Drum Island, Vivi in Alabasta, etc. And the other characters central to the plot in that particular arc as well. Usually the motivations of the villain are done extremely well and the way the island is introduced, each character, the progression of the story are nicely done. My main gripe is whatever happens in the last third, the fight with the bad guys, One Piece has always been lacking in the action department. By that I mean while there's plenty of action(emphasis on plenty), it's never exciting since it's not directed and animated all that well, especially post-time-skip. Be it in Fishman Island, Dressrosa or Wholecake.
That's where Naruto is far better, the action itself is probably among the best in all anime and is always extremely exciting, cool and visceral.
I like the soundtrack a lot better as well, and in general Naruto is probably a lot cooler, be it the powers, the combat or the characters.
