I like Britney Spears and Jessica Simpson. I see Katy making fun of them calling them old, fat and over the hill. Besides they never could sing anyway, at least not like Katy. And of course Katy also makes fun of Jessica's apparent lack of intelligence.
I don't see Britney or Jessica vicious enough to pull this off, I think of them team as the modern day Southern Belles of G.L.O.W. They need a more cruel partner to have any chance of winning against Katy.
I like the Olivia Wild & Megan Fox team Fox in the Wild destroying Katy.
Madonna & Lady Gaga seems pretty natural although I really like Lady Gaga & Nicki Minaj together as a small psycho pair.
Taylor & Hayley is pretty interesting although I don't know Hayley's personality.
Rihanna & Beyonce is a good team even though they are natural rivals.
Janet Jackson & Madonna would be a decent match up if you wanted to go older destroying younger.
Still my favorite is the Lady & Nicki for some reason, that seems to intrigue me the most.
How about three rappers Foxy Brown, Lil Kim & Nicki Minaj giving Katy a thorough beating.