Mirror match ups. You can automatically dismiss anyone who has a role in both crews.
Luffy v. Blackbeard
Chopper v. Doc Q
Usopp v. Van Auger
Jinbe v. Jesus Burgess
Nami v. Lafiette
All of these characters have identical roles, in a show that hasn't tried to push crew roles outside the Straw Hats ever.
Zoro v. Shiryuu
Nico Robin v. Catarina Devon
Both of these are agiven, seeing as how Shiryuu shares many similarities with Zoro, especially how they both joined their crews. Catarina Devron also emphasized (or Oda did in a SBS) hunting down pretty women to kill. Nami is going against the opposing Navigator, so that leaves Robin.
Franky v. Sanjuan Wolf
Brook v. Vasco Shot
Sanji v. Pizzaro
Franky and Wolf is the most solid out of these ones. They're more process of elimination + loose connections. Sanjuan Wolf is known as the "Colossal Battleship" and we're seeing that Franky is fighting with a mech suit more and more, so it's not unreasonable to say he might fight with the Thousand Sunny or another large construct.
As for the other two... Pizzaro seems ambitious, has a North Blue connection, was a King/Royalty. And was the only Impel Down member outside of Shiryuu to have a unique set of clothing on instead of prison stripes. That makes him stand out quite a bit. If you wanna think of what crewmate deserves such a unique opponent, it's Sanji. Add in royalty connections and one towards North Blue? Yeah, seems likely with our current knowledge.
Vasco Shot and Brook? Well, Brook's always telling dumb jokes and Vasco looks like a jester. That and every other fight seems to have something to it.
Luffy v. Blackbeard
Chopper v. Doc Q
Usopp v. Van Auger
Jinbe v. Jesus Burgess
Nami v. Lafiette
All of these characters have identical roles, in a show that hasn't tried to push crew roles outside the Straw Hats ever.
Zoro v. Shiryuu
Nico Robin v. Catarina Devon
Both of these are agiven, seeing as how Shiryuu shares many similarities with Zoro, especially how they both joined their crews. Catarina Devron also emphasized (or Oda did in a SBS) hunting down pretty women to kill. Nami is going against the opposing Navigator, so that leaves Robin.
Franky v. Sanjuan Wolf
Brook v. Vasco Shot
Sanji v. Pizzaro
Franky and Wolf is the most solid out of these ones. They're more process of elimination + loose connections. Sanjuan Wolf is known as the "Colossal Battleship" and we're seeing that Franky is fighting with a mech suit more and more, so it's not unreasonable to say he might fight with the Thousand Sunny or another large construct.
As for the other two... Pizzaro seems ambitious, has a North Blue connection, was a King/Royalty. And was the only Impel Down member outside of Shiryuu to have a unique set of clothing on instead of prison stripes. That makes him stand out quite a bit. If you wanna think of what crewmate deserves such a unique opponent, it's Sanji. Add in royalty connections and one towards North Blue? Yeah, seems likely with our current knowledge.
Vasco Shot and Brook? Well, Brook's always telling dumb jokes and Vasco looks like a jester. That and every other fight seems to have something to it.