¿Who is stronger, Vegito or Onslaught?

Vegito is a prominent fusion character in the "Dragon Ball" series, resulting from the Potara earring fusion of Goku and Vegeta. This fusion combines their strengths, resulting in a warrior of exceptional power and skill. Vegito first appears during the "Majin Buu Saga" in "Dragon Ball Z," confronting Super Buu to rescue absorbed allies. In "Dragon Ball Super," Vegito reemerges as Vegito Blue, utilizing the Super Saiyan Blue transformation to battle the fused antagonist, Zamasu. His abilities include the Final Kamehameha, a fusion of Goku's Kamehameha and Vegeta's Final Flash, and the Spirit Sword, an energy blade technique. Vegito's fusion, achieved through the Potara earrings, was initially believed to be permanent; however, it is later revealed to last one hour for non-deity beings. Throughout the series, Vegito exemplifies the combined might and strategic prowess of Goku and Vegeta, making him a formidable force against powerful adversaries.

Onslaught is a comic book character created by Marvel Comics and is known to be one of the publisher's most powerful and feared villains. He is a cosmic being created by merging the minds of Charles Xavier and Magneto, two of Earth's most powerful mutants. Onslaught has a number of supernatural powers, including the ability to manipulate people's minds and behaviour, superhuman strength and the ability to manipulate magnetism. He is also virtually indestructible, making him a formidable foe for any hero who confronts him.