I like both , Katy and Rihanna.
But if you want to compare them you have to consider all the facts.
And Katy has 2 almost 3 number 1 hits from the same album.
Rihanna is doing amazing this era.
But she has been around since 2005.
And has hits with Eminem, T.I. (in his best moment), Jay Z, Drake (in his best moment).
I'm not saying she doesn't deserve it. Of course, she's talented and great artist.
But i think this is Katy Year as Female Artist.
Tres HUGE succesful singles (one featuring Snoop it's true but it's a Katy song) and a #1 album that is selling (not millions, but it's selling good) and plus a grammy nomination for album of the year.
Maybe Rihanna will be in the same conditions with her next single.
