You could make a good case for any of them tbh.
On a long run, it's Luffy cuz he beats the biggest villain of the arc.
When it comes to short crucial moment, Sanji saves Momo from King which could have ended in the alliance's defeat if he dies.
Marco stalls Big Mom, King and Queen for a good amount of time which prevents further casualties.
Tama's DF turns the tie for the ground troops to fight back.
Yamato stalling Kaido on the roof.
Etc.
On a long run, it's Luffy cuz he beats the biggest villain of the arc.
When it comes to short crucial moment, Sanji saves Momo from King which could have ended in the alliance's defeat if he dies.
Marco stalls Big Mom, King and Queen for a good amount of time which prevents further casualties.
Tama's DF turns the tie for the ground troops to fight back.
Yamato stalling Kaido on the roof.
Etc.