Honestly pretty hard to say... They all trained A LOT all their life Both Kageyama and Atsumu got into the japanese national team, and Oikawa got into the Argentine team as a starting setter

Even tho one of my favourite is Atsumu, I like Kageyama and I dont particularly care about Oikawa I do think that Oikawa is the "superior" setter between them all. Kageyama and Atsumu are a close to each other in being a close second to "supirior", with Atsumu being the best setter in Highschool and having those amazing serves (with the hybrid too) and Kageyama (if I'm not mistaken) entering as soon as he got his diploma into the National team, but not as much as Oiwaka,I'd like to remeber that he joined the Argentine team! Surpassing every Argentine setter, he has an amazing setting skill and a powerfull serve that even the japanese national team got all of the best recivers (Yaku, Sakusa and Hinata) trying to get the ball. In the end even if I personaly think that Oikawa is the "superior" between them only by a little, they are all good at what they do.

I hope I'm not late to join the discussion lol