It's likely Goku. His Super Saiyan forms give him incredible power levels that far exceed most of the characters in One Piece. He can move at incredible speeds, has amazing strength, and can fire powerful energy blasts. Even Luffy in his Gear Fifth form would probably have a hard time against Goku at his full power.
Well, it's a tough call, but if we consider the potential of the characters, it could be Vegito. If Vegito were to enter the One Piece universe, his combined power of Goku and Vegeta would be almost unstoppable. He could easily take on the strongest pirates and even the admirals of the Marines. However, the Devil Fruit powers in One Piece are also very diverse, so it's not completely clear - cut.
Goku and Luffy would be really interesting. Goku is all about pure strength and the pursuit of becoming stronger through training, while Luffy is more about the adventure and his dreams. Their different outlooks could lead to some great conversations and also some funny moments, like when Luffy tries to eat Goku's senzu beans thinking they are some kind of food from his world. Another interesting interaction could be between Vegeta and Zoro. Vegeta is very proud and serious, and Zoro is a swordsman with his own code of honor. They could have some intense sparring sessions and also respect each other's strength.
Zoro and Vegeta would also be a cool pairing. Zoro is all about becoming the greatest swordsman and has a strong sense of pride. Vegeta is a proud Saiyan prince. They could start off as rivals, constantly trying to outdo each other in combat. But as they face tougher enemies together, they would start to respect each other's skills. Vegeta could teach Zoro some energy - based attacks to add to his swordsmanship, and Zoro could show Vegeta the value of discipline in a different way.
Well, if we consider that in the Sonic universe, there are characters like Shadow who has his own unique abilities and is very powerful. In a crossover, if he were to gain some of the Saiyan abilities like ki control, he could be a formidable force. But then again, Vegeta with his pride and combat experience wouldn't be one to back down. He might be able to figure out Sonic's speed patterns and counter them. So it's not easy to determine who would be the most powerful. It could also be a new character that emerges from the combination of the two universes' power sources.
It's hard to say, but Goku would be a top contender. His ability to constantly increase his power level and learn new techniques would make him a force to be reckoned with, even in a world with Pokemon. He could potentially use his Ki to enhance the abilities of any Pokemon he teams up with.
If we consider the potential of power - up in a crossover, it might be a new form of Goku. Imagine if Goku were to combine the power of the Saiyan God form with some of Devilman's demon - like abilities. He could become an entirely new and extremely powerful entity. But then again, Devilman has the potential to merge with other powerful demons in his world. So, in a sense, it could be either Goku with his new form or a super - powered Devilman depending on how the fanfiction unfolds.
Aizen Sousuke is another character from Bleach who could be in the running. His intelligence and his hogyoku - enhanced powers made him a formidable foe. In a crossover with Dragon Ball Z, if he were to face someone like Frieza, he could use his illusions and mind - games to gain an advantage. Frieza is powerful but not as mentally cunning as Aizen. However, if Frieza were to transform into his final form quickly and catch Aizen off - guard, Frieza could potentially win. So again, it depends on how the fight unfolds and who can utilize their powers more effectively.
Well, it could be Whis from Dragon Ball Z. He is an angel who is extremely powerful and has knowledge of many things. In a crossover, his powers would be far beyond what most characters in Bleach could comprehend. He could potentially manipulate the very fabric of the Bleach universe with his angelic abilities. Even compared to Goku and Ichigo, Whis' level of power is on a different scale. He could be the most powerful if he were to get involved in the events of the crossover.
It's hard to say for sure, but Goku would be a very strong contender. His ability to keep increasing his power level through training and reaching new forms like Super Saiyan God and Ultra Instinct makes him extremely powerful. However, characters like Franklin Richards in the Marvel universe have reality - warping powers that could also be very hard to defeat. But if Goku were to fully master Ultra Instinct and combine it with the power of the Dragon Balls, he could potentially be the most powerful.
Well, if we consider all the characters from both universes combined, it's hard to say for sure. Goku is obviously a top contender with his godly forms and limitless power potential. But then there's also characters like Whitebeard from One Piece. He had the power to cause massive earthquakes and was feared across the Grand Line. If he were to somehow gain access to Ki or some form of Dragon Ball Z - like power - up, he could be just as strong as Goku. And let's not forget about Vegito, who is a fusion of Goku and Vegeta. His combined power is off the charts, and in a combined universe, he would be a force to be reckoned with as well.
A very powerful pairing could be Whis and Odin. Whis is an extremely powerful being in the Dragon Ball Z universe with near - omnipotent powers. Odin is a powerful Asgardian god. Together, they could use their vast knowledge and powers to manipulate time, space, and reality. They could prevent disasters in both the Dragon Ball Z and Marvel universes or deal with threats that are too powerful for any single hero from either universe to handle.