I think they're on the same level of popularity.

I'd have to check their sales but K$ singles do way better than Taylor in America and overseas, look at TT numbers.

I'd definitely go with Taylor. She's moderately successful in Asia, and despite her tour dates were mostly in the U.S, she didn't have any troubles selling out concerts overseas. And she has sold 20M albums worldwide.

Taylor's music is more... American, so Ke$ha obviously. That's not saying Tswift isn't more successful in general.
edit: i forgot about touring, so I answered TS.

Taylor Swift

I would say Ke$ha's singles are probably bigger worldwide, but Taylor's album sales are pretty good WW plus she recently got back from a very successful world tour.

Her Fearless album is 9x platinum in the Philippines

Taylor trumps Ke$ha in the US, which is Ke$ha's only market aside from maybe Canada and Australia.. So Taylor.

Ke$ha's album sales and single sales are more global.

Animal
CertificationsCountry Certifications
Australia 2× Platinum[36]
Austria Gold[88]
Canada 2× Platinum[32]
Germany Gold[89]
Ireland Gold[90]
Japan Gold[91]
New Zealand Gold[39]
Poland Gold[92]
United States Platinum[28]

Fearless
CertificationsCountry Certification
Australia 5× Platinum[79]
Canada 4× Platinum[77]
Ireland 2× Platinum[91]
Japan Gold[85]
New Zealand 2× Platinum[81]
Norway Gold[139]
Philippines 9× Platinum[86]
Russia Gold[140]
United Kingdom Platinum[89]
United States 6× Platinum[72

Taylor.

Just because your album sells more doesn't mean you are more global.

If the sales were close I'd agree but when you have more than 2 or 3 million album sales than someone I think its safe to say your bigger

Bigger in the US, where majority of her sales come from.

Philippins =/= Asia.

Neither are that huge but people have at least heard of Ke$ha. Taylor is so local.