Well, Naruto world. The concept of chakra and stuff would fit better for me.
In One Piece world, it is extremely difficult to become one of the stronger ones there. And haki is really hard to acquire.
i like one piece more but i would prefer to live in the naruto world because it´s easy to get stronger steal a bloodline limit or bring dead people to life to fight for, you like somebody above me said it´s hard to be a top fighter in op