I'd have to go with Takehiko Inoue, dude has two top tier mangas in completely different genres. He made arguably the greatest sports manga, and the greatest martial arts/action manga. Excelling at the highest level with two completely unrelated demographics speaks for itself. It also doesn't hurt that his art is arguably the best in the entire medium, and his storytelling hardly lags behind. He basically checks all boxes, it's hard to see anyone else (that I'm aware of) edge him out in this discussion imo.
Honourable mentions to the others who have had success with multiple manga, Togashi and Urasawa. And I think Oda deserves massive credit for drawing for over 2 decades without any major breaks, that's a major feat.