People voting for Rih obviously haven't seen her recent album sales or / and are forgetting her yearly November album debut numbers & her tour attendance in the USA and in some cases price of the tour tickets.
Anyways, currently Katy. Overall, Taylor Bey and Gaga.
5 consecutive #1s, another top 3, another #1, 3 VMAs, 5 PCAs, 1 AMA, a #1 double platinum album that is continuing to sell almost two years after its release, almost 30 million records sold in the US alone in under two years, selling out venues across the US on her first arena tour, etcetera.
Current success?? Certainly Katy. Over 2.1 million albums sold. 3 5-million, 1 4-million & 1 3-million selling number ones. 2 more extremely successful singles. She's outlasted every other big name's era(Britney, Bey, Adele, GaGa, Ke$ha & 2 Rihanna eras).