I see Britney and Christina as the Sidney and Gale of the music industry tbh

Christina would die first because no one wants to watch an ugly fat chick for the entire movie.

Katy would die next because she's the uninteresting brunette who is only killed to show this is a serial killer, and not a one time offender.

Beyonce, Rihanna or Nicki would be next because it's a safe place to put the mandatory black death without coming across as bluntly racist.

Rihanna would die next (If she didn't die from the third round of killings) because there's always a drugged person killing, in an attempt to show the younger audience that they're edgy and happenin'.

GaGa would be next because they always kill the unpopular weird kid suspected of being the killer to throw the veiwer off.

Katy would be stabbed a few more times because the public would enjoy that.

Ke$ha and Kelly would be the last ones left, but Kelly would fall and die in the big chase scene because she's slower.

So I guess my answer would be Ke$ha, Queen of everything.

Brandy would be the killer.

The dragging