I've never seen the Kats and the Navy go at it like this.

I guess Rihanna is the IT Girl right now. She has been pitted to basically anyone right now, just like with Taylor earlier this year.

I don't know about the whole world, but where I live Rihanna is bigger.

Rihanna >>>>>>> Katy.

In every category possible except for breast size.

Rihanna by a mile.

Katy's the bigger WW touring act, so if she manages to keep that up she can and will be the more global artist.

Rihanna has a stronghold on Europe, but even so Katy's doin just fine over there while having it even better in the US/Aus.
Rih has the Carribean on lock and it's that influence alone that impacts music worldwide.
Tbh it's hard to say but I'm sticking with Katy on this one.