I'm not saying chart success means nothing, because it does, but tour demand > single sales.
EDIT: And album sales might not be a strong point here, since Born This Way and Teenage Dream aren't that far away from each other when it comes to sales (Considering Katy had bigger singles and a re-release)
I think Gaga because I don't see Katy selling out such hell lot of pricey tickets nearly as effortlessly,ever.Gaga is the more known and respected PERFORMER.If we're comparing their total success while also keeping in mind that Gaga has an EP more,Gaga ***** all over Katy.Teenage Dream and Born This Way have had similar success album sales wise but singles wise clearly TD is far superior.
But I can't at Gaga stans screaming 'I CAN'T!INVALID COMPARISON!'.Katy's popularity has actually grown a lot and her next tour will stay far from touching Gaga's tour success but will probably do a lot better than CDT,and her latest album has actually outdone Gaga's latest overall.Both have points in favour,I don't see why you think it's SO obvious that Gaga is bigger.
It's all fine looking at the peak of single sales, lets look at the actual sales from each single right from the start. I find the starter of this thread won't do that.
What biased opening. Try again. Definately Gaga and the UK agrees.