I find Xtina a very underrated performer(tbh she is an underrated popstar as well). She actually put on a great show when she is up on the stage. She has better performances than this one though
Britney is overrated for me. Sure at her prime she danced her ass off. But that was it. It was quite boring. Also, this I'm Slave For You performance is SO overrated(like the song). It's ok but nothing special.... Sure she has a snake and all that but that is it. Not even gonna talk about her performances nowadays
GaGa is a solid performer. It's been a while since she putted a show stopper one. The Paparazzi performance is also overrated.
That being said:
GaGa > Xtina > Britney