Leonzky
If we talk about a manga that can boom on a large scale immediately, it would be Shumatshu no Valkyrie. I still remember how it easily gained popularity, and the author could change the fights or the list of names and more examples, etc. And another manga could be Dr Stone because it is quite different from other shonen and it is complete. This is also my recommendation and my point of view. PS: I like your fanfic, keep it up
The big 3 won't have an instant good reception because it requires a lot of chapters for them to start being good. Same with Attack on titan, this should be the 2n manga. You can start with One Punch Man because it has a different concept than usual, story is good, characters interesting but not too complicated and its comedy is decent. Otherwise Solo Leveling for its top art but I wouldn't do it because then the fans will expect all mangas to be colored