They have both made a huge impact but i think musically Britney only because her sound has been consistently more focused in one genre. She progressively pushes pop to new levels, while others are always bringing up influences from the past.
And Britney has more impact in both the positive and negative sides, for those asking in what way. In her prime, the breakdown, and the comeback. People still love Britney. Everything not just about the ATRL creatures.
The both have had a huge impact in music. They are both equally icons/legends in their own way. But Britney Spears is slightly ahead in the Impact department. Britney is bigger world wide. Britney impact not only changed pop music, but it also changed pop culture. So Britney
