I thought a while back but I couldn't find a wuestion…
Who will be the strongest opponent each of the Mugiwaras has to face???
Ok three are probably clear...
Luffy - Whitebeard, Dragon, Shanks or Ao Kiji
All of them were introduced as super powerful pirates... Whitebeard called the strongest pirate... Ao Kiji the strongest marine... Dragon his father the worst criminal of the wordl... maybe there will be a reason ti fight and Shanks just cause of the relationship
Zoro - Mihawk or probably Shanks
Mihawk the strongest swordsman but there is nothing clear about Shanks... but I think when they fight against Shanks than Luffy will do ist...
Ussop - Lassop or Van Auger
Lassop is known of the best sniper in the whole grandline but Van Auger ist still amazing!
but for the others I don't find any other... Most of common is Sanji (not cause I'm a fan) He is one of the Top 3 fighter and he should have someone who will be his ultimate challenge... ok his dream isn't to become the strongest but he was always be shown as equal or a bit below Zoro so he should get one...
I thought maybe against Lucky Roo... cause of the speed... but I think his position is too low to be an ultimate challgene when you look at Zoro's or Luffy's opponents...
For Nami, Robin, Chopper and probably Franky I have no clue... Maybe you get one???