¿Who is stronger, Onslaught or Buu?

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.

Majin Buu is a pivotal antagonist in the "Dragon Ball" series, introduced during the "Majin Buu Saga" of "Dragon Ball Z." Created by the dark wizard Bibidi, Buu is an ancient entity with immense power and a malleable, pink physique. Throughout the series, Buu undergoes several transformations, each altering his personality and power levels, including Innocent Buu, Evil Buu, Super Buu, and Kid Buu. His abilities are vast and versatile, encompassing regeneration, absorption, and transmutation, such as turning adversaries into sweets. Despite his initial role as a villain, aspects of Buu's character, particularly in his Innocent form, display a capacity for change and even benevolence. This complexity adds depth to his character, making him one of the most memorable antagonists in the "Dragon Ball" universe.