This is a pretty close fight, but in the end Usopp wins. He has a fire blast that he can shoot from his staff type weapon. With it even Nami’s lighting and weather staff can’t prevail. Usopp wins.
Luffy can beat Usopp pretty easily. Usopp once tried to usurp leadership and it didn’t end well for him. Luffy is too strong and has Gear 2. That form works the same way as Super Saiyan. It multiplies his power. Luffy wins.
Zoro has sword skills that he can use to slash through the strongest defenses. No one can stop him. Usopp can try but in the end he’s not in Zoro’s league. Zoro is quite possibly the strongest Pirate in the Great Seas. Zoro wins.