Bey. Even if R&B isn't as popular in places like Europe or Asia, she's still one of the biggest names in Pop/R&B in those parts. Shes also been around longer and has a more diverse demographic of fans.
The both did...But Beyoncé is HUGE in Europe especially in the UK and Nederland. She is selling out stadiums left and right in Europe and R&B isn't popular at all over here.. So she's selling only due to her name alone. And I think that if she takes the FWT in Australia, Asia and Latin America the arguments will be over.
Next era Taylor will grow and be bigger WW and could eventually be as big as Beyoncé...I'm from europe so that's my perspective.