Katy Perry vs. Britney Spears Singing "Passenger"

Britney Spears released the song "Passenger" back in 2013.  Katy Perry actually co-wrote it, and recorded a demo for it before giving it up to Britney.  That demo has now leaked.  This video compares to two singing their versions of the sing, and Sia's version is thrown in there, too, just for kicks.  Whose version do you like best?