Rihanna and her endless bops?
Katy Perry and her tailor-made-for-pop-radiomusic?
Taylor and her +1M debut albums?
Lady Gaga and her Artpop?
(I didn't include Beyoncé, Britney or P!nk cause they've been in the industry the longest. Oh, and I don't care enough about the other popgirls, if I missed any.)
Taylor already releasing records for 8 years now and bigger than ever. She is also younger than the others in the poll. She has more scope for longevity than the others.
Probably Rihanna since she still has a few eras left before she hits 30. Taylor, too, for the same reason. Katy will still be around for a few more years.
I see Taylor around for a bit longer since she writes her own music. Katy and Rih will get old and lose thier sex appeal and musuc producers and writer will gear towards a new sexy young popgirl. Gaga, I have a feeling that she still have some success left in her.