Katy knows how to hit people with the right kind of material. Catchy hooks, euphoric lyrics and strong melodies are the three necessary factors you need to sustain yourself in the pop game these days. Gaga lags behind in that respect, at least judging from her last record anyway. Gaga will probably sell more albums, but the next era from Katy will likely have a bigger impact on popular culture as a whole. People will look back and reminisce, just like they do with Teenage Dream.
Katy will probably have higher selling singles. Gaga will obviously have a larger grossing tour. Album sales, I'm not sure, they might end up pretty close to each other like last time.
