Britney was obviously more successful (not saying Bey wasn't, because she was as well) in the 00s. Can we move on now?
I pick Rihanna + someone new. Rihanna will have a solid decade, and the new girl will probably emerge halfway through. I love all of the new girls trying today, but I don't know if the public is here for them.
As of right now, it seems like Rihanna and Gaga are the front-runners. However, I'm not entirely convinced that 1 year in we can say for sure.
I'll go with Rihanna cause she has more possibility for longevity, Gaga's image is too risky to get sick of. However, if she reverts to her The Fame or The Fame Monster style, she certainly will easily be the #1 pick.
Rihanna. She's not even 24 and has at least 5 more years at her availability.
She'll last longer than 5 years I hope. But she has consistently sold extremely well since she started, yet isn't normally refereed to as the Queen. My bets on Gaga or someone new.
Britney was not more "successful" than Beyonce during the 00s. Selling more albums =/= being more successful, so let's nip that right in the bud. You claim Britney is the Queen of 00s yet who actually called her that? Oh, nobody. Also, there is no legitimate worldwide publication to rival Billboard (who already named Bey the Queen of the 00s multiple times) so there is really nothing to debate.