I feel like you can’t compare them considering how long One Piece has been out and how new My Hero Academia still is. A lot can happen in My Hero to make it flop.
Concept wise, One Piece is more unique. However, I find My Hero Academia easier to digest. In that case, I find the my hero is more straight forward written, using a lot of storylines that are common in western comics (which I’m a huge fan of).
One Piece does get more creative in some of its arcs. And obviously it must be doing something right, considering how many mangas it’s sold and how the anime is still on going. Using sales logic, then One Piece is better.
I think In the end it comes to preference. I like my Hero because of the nostalgia it gives me since it’s very reminiscent of western comics.