Hm, this is a hard one. One thing i am sure is that Leo would not be able to beat either Noelle, Nozel or Fana.
Noelle is Leo's counter and she probably has one of the highest magic power in the Clover Kingdom, which gives her attacks the sheer force and power that Leo probably would not be able to handle.
Nozel is a captain level combatant with lots of experience, and he has a tactical mind. Leo wouldnt stand a chance.
And Fana probably wouldnt even be fazed by his fire magic. I doubt you could fight fire with fire, and even if he would make a dent or damage her somehow, her regen is just insane.
I think if it werent for Jack back then, Noelle would not have been able to beat Fana. And even when Jack joined they still werent able to beat her. Fana was able to keep up with Valkyrie Armor, which means she has also speed. And despite Jack joining they werent able to damage her despite Jack's op ability. Her regen is kinda insane.
Current Noelle should definitely be stronger now, but i still doubt if she would be able to beat Fana cuz of her insane sustainability. Maybe if she made an attack so massive that could blow away Fana's entire body along with the grimoire
i really dont know, this battle royal is tricky
the logical answer would be Nozel and Noelle, but hm .... Fana