Roar was bigger than Applause
Uncle was bigger than Judas (at least in the US)

Dark Horse was bigger than TEOG
You and I was bigger than Birthday
TIHWD was bigger than MTN
BTW the album sold more
BTW received stellar reviews, PRISM was more on the mixed side
Too early to compare the tours
Conclusion
Katy had the bigger singles by far bc of Roar and DH
Gaga had bigger album sales and reviews
But it feels like most people are still into Katy, unlike Gaga towards the end of the BTW era
So Katy wins imo