Naruto

Any answer that isn’t One Piece is wrong.

Nah, One Piece is just......

You haven’t even seen it, you can’t say anything. From the options here though, it has by far the most explored, fleshed out and expansive world, and I honestly don’t think things like Bleach and Black Clover have that great of worldbuilding.

One Piece is just… built different when it comes to worldbuilding.

From this list HunterxHunter, but I think Naruto

HxH. From what I’ve seen of one piece the world building was good but HxH’s is better. Mind you I haven’t seen all of one piece.

I think, of the anime I’ve seen, the best are Fullmetal Alchemist Brotherhood and Last Exile. Both of those do a good job of focusing in on one place or ship in the world while still fleshing out what lies beyond.

Hunter x Hunter

I'll go with Hunter x Hunter. I haven't watched One Piece yet.