I've already watched the performances again...I swear I tried it to vote for Beyonce but I couldn't
Beyonce: Vocally was better, but overall the song doesn't fit to her at all, and she doesn't know how to be a rocker, the way she was shaking her hips and hair and the very feminine outfit with high heels, anything fit right with the song..... Vocally she was better than Brit but she gave a very corny / cheesy performance of the song to be honest.
Britney: Though Bey had better vocals, Brit's vocals weren't bad either and actually were more similar and suitable to Alanis vocals .... the outfit , her attitude on the microphone with sun glasses, were very suitable with the song and performance overall, and she had a little bit more touch of Rock than Bey's.
so at the end I voted for Britney's.