Beyonce tbh.
She has probably the best marketing campaign and presence as far as serving good face in the media and it would be really easy to think she is the one outselling her peers in totality and scoring more #1s/top 10s and breaking those type of records based on how they market her to the media; however, when you look at the actual stats its less than what is pushed out there.
I was going to say miley but I checked her stats and I guess she kinda slayed a bit with her hannah montana days.
the others: Katy and Rihanna are big single sellers...that's known to the public
gaga and taylor kind of do both and gaga is in a low point at her career right now...I think the public gets that
Ariana...I don't think they check for her stats
Britney is obviously the top selling in totality and doubt any GP person would be surprised.
So yeah