It's really hard to say. Naruto has the power of the Nine - Tails and his Sage Mode, which makes him extremely strong. But Luffy has his Gear Fourth and his ability to stretch and resist attacks. However, if we consider someone like Madara Uchiha from Naruto, with his Rinnegan and vast combat experience, he could be a top contender. But then again, there's Whitebeard from One Piece who was incredibly powerful. So, it really depends on how the crossover is written and the situation in the story.
It's really hard to say. Luffy has his rubber powers and Haki which can be extremely powerful. But Naruto has the Nine - Tailed Fox and his vast array of jutsu. If they combined their powers, they would be a force to be reckoned with. However, if we consider villains, someone like Madara Uchiha with his Sharingan and all his skills, if he got his hands on a Devil Fruit, he could be extremely dangerous. But then again, Kaido from One Piece is also super tough. So, it's a tough call.
I think it might be a toss - up between Goku (just kidding, not really part of the crossover but for comparison). Seriously, though, it could be Kaguya from Naruto. Her powers are almost god - like with the ability to create dimensions and control time. In the One Piece world, there's not really anyone who can directly counter those abilities. But then again, Im from One Piece has a lot of mystery around him and could potentially be extremely powerful. If Im had some way to nullify chakra, he could be the most powerful in a crossover situation.
It's really hard to say. Luffy has his Gear Fourth form and the ability to stretch his body in incredible ways. But Naruto in his Sage of Six Paths mode is extremely powerful too. He has access to a vast amount of chakra and can use some of the most powerful jutsu. However, if we consider Kaido from One Piece, with his near - indestructible body, he would also be a top contender. So it could be any of them depending on how the crossover is written.
It's hard to say for sure. Luffy has the power of the Gum - Gum Fruit and his Haki, which gives him great strength and the ability to sense and overpower opponents. However, Naruto has the Nine - Tails' chakra and Sage Mode. In a crossover, if they were to fight, it might depend on the situation. But if we consider all - round power, Naruto's ability to create multiple clones and use a variety of jutsu might give him an edge over Luffy in some scenarios.
Sasuke merged with Zoro could also be very strong. Sasuke's Sharingan and his various ninjutsu like the Chidori, combined with Zoro's three - sword style and his great swordsmanship skills. The Sharingan could help Zoro predict his opponents' moves even better and Sasuke could use Zoro's physical strength to enhance his own attacks.
I think it could be a toss - up between Goku and Whitebeard. Goku has his incredible ki attacks and speed, but Whitebeard had the power to cause earthquakes and was considered one of the strongest pirates in the One Piece world. If Whitebeard were to face Goku, his experience and the power of his Devil Fruit could potentially give him an advantage, especially if he caught Goku off - guard.
It's a tough call, but it could be Luffy. His Devil Fruit powers combined with his indomitable will make him extremely formidable. If he were to somehow gain some Soul Reaper abilities on top of that, like the ability to use a Zanpakuto, he would be near - unbeatable. His Gear Fourth form already gives him enhanced strength and speed, and with Soul Reaper powers, he could be a force to be reckoned with.
Dumbledore might be the most powerful. He has vast magical knowledge and experience. In a crossover, he could quickly understand the mechanics of Devil Fruits and use his magic to counteract any threats from One Piece characters. He could also use his intelligence to outwit the pirates and use spells like the Patronus to protect himself and others from danger.
It could be Naruto himself if he fully utilizes the gamer abilities. With his already strong will and determination, combined with the ability to quickly level up and gain new skills from the gamer aspect, he could become extremely powerful. He has the potential to master all kinds of jutsu faster and use them more effectively in battles.
Naruto has a strong case for being the most powerful. His Nine - Tails chakra mode makes him incredibly strong, fast, and durable. He also has a vast array of ninjutsu at his disposal. In a crossover, he could potentially learn to use Ichigo's reiatsu in some way, making him even more powerful. Plus, his never - give - up attitude could give him an edge in a tough battle against Ichigo.