I used to think it was equal between Gaga and Rih but now I'm 100% sure it's Gaga. Why?
1) Gaga is a huge force in Asia and the fact that she might outgross her peers with just the Asian leg of her tour shows that.
2) Rih has scored more hits in the U.S., but her album sales and the price of her tour tickets sometimes show that Americans don't really care about her.
3) The fact that Rih lost a Brazilian poll (Rock In Rio) against Katy and the Loud Tour didn't really sell that much in Brazil (most vital country of Latin-America).
4) Europe's not the world.
So Gaga.