It could be Kirito. He has a lot of combat experience from SAO. If he teams up with a strong Digimon like Omnimon, he would be extremely powerful. His sword - fighting skills combined with Omnimon's attacks would make them a formidable force in any battle.
However, there's also the option of a Digimon like Imperialdramon. If it were to somehow gain the knowledge of the SAO world and its combat strategies, it could potentially be the most powerful. It has huge physical strength and powerful energy attacks that could overpower most opponents in both the Digimon and SAO universes.
Asuna could also be a top - tier character. She's very skilled in SAO. If she were to bond with a Mega - level Digimon like Rosemon, they could be a powerful duo. Rosemon's flower - based attacks and Asuna's agility would be a great combination.
Arceus from Pokemon and Omnimon from Digimon are both extremely powerful. Arceus is like a god in the Pokemon world, creating everything. Omnimon is a powerful Digimon formed by the fusion of WarGreymon and MetalGarurumon. If they were in a crossover, it's really hard to say who would be more powerful. It might depend on the situation and how their powers interact.
It could be Sailor Moon herself. Her powerful magic and ability to transform could give her an edge. She has the power of the Silver Crystal which is extremely potent. When combined with the powers of a strong Digimon, she would be nearly unbeatable.
There's also the possibility that a new character created through the Xros of a Digimon and a ninja could be the most powerful. Imagine a Digimon that has absorbed Naruto's chakra and can use it to enhance its attacks. This new hybrid character could have unique abilities that neither the Digimon nor the ninjas possess on their own, making it a very powerful entity in the fanfiction.
Sinon from Ggo could also be very interesting. If she were to enter Sao, her sniper skills might translate in unexpected ways. She could be paired with characters from Sao and learn new combat techniques while also teaching them about the precision of long - range attacks.
I think Naruto and Kirito would be an interesting pair. Naruto is all about his exuberant and determined personality, always believing in his strength and the power of friendship. Kirito, on the other hand, is more of a lone wolf type at first but also has a strong sense of justice. Their meeting could lead to some great character development for both. Naruto could teach Kirito about the value of relying on others more, and Kirito could show Naruto some advanced combat strategies that he has learned in SAO.
Another interesting pairing could be Yolei and Rika. Yolei is very tech - savvy and has a strong will. Rika is a tough girl who is also really good at Digimon battles. They could bond over their shared interests in technology and Digimon, and maybe have some friendly competitions to see who has the better Digimon strategies.
Naruto and Agumon would be a great pairing. Naruto's energetic and fearless nature would mesh well with Agumon's loyalty and eagerness to fight. They could both learn from each other's determination in battle.
Sasuke and Renamon would also make a great pairing. Sasuke's brooding and intense nature could be complemented by Renamon's calm and collected demeanor. Renamon's intelligence and combat skills could match Sasuke's Uchiha abilities. They could have some intense training sessions together, where they both learn new techniques from each other.
Omnimon could also be a very powerful partner for Naruto. Omnimon is a super - powerful Digimon resulting from the fusion of WarGreymon and MetalGarurumon. Naruto's ability to make friends and work in teams would be perfect for handling Omnimon's complex nature. Together, they could take on any enemy in the fanfiction world.
It's really hard to say. Naruto in his strongest form, like when he has the power of all the tailed beasts, is extremely powerful. He has incredible strength, speed, and the ability to use a vast array of jutsu. However, Aang in the Avatar state has access to all four elements and can be a formidable opponent. If we consider the Avatar state's spiritual connection, it could give Aang an edge in a battle of wills.