I ranked them worst to best in my opinion:

Performing:

Nicki Minaj
Ke$ha
Britney Spears (now)
Rihanna
Jennifer Lopez
Katy Perry
Christina
Beyonce
Gaga

Bey and Gaga are basically even to me, but because Gaga actually switches it up and is geniune in my eyes, she stretches ahead

Talent:

Nicki Minaj
Rihanna
Britney Spears
Jennifer Lopez
Ke$ha
Katy Perry
Christina
Beyonce
Gaga

Once again, Bey and Gaga are close, but because Gaga writes all of her music and can play instruments, she stretches out ahead..