I think greenbull next one, since he need to beat beat up by luffy to change his mind .
‘For true 1 vs1 fight like katakuri style.
I believe it will take place in elbaf with Norse mythology stuff, I am thinking luffy gear 5 vs greenbull forest form should be cool.
‘Since greenbull is already goofy character. He is good character fot luffy to fight. His villain style is literally Saturday morning cartoon villain type.
I don’t think shanks will fight luffy since oda want to portray him as good guy.