Britney is purely a merchandising product, with minimal talent, and marginal attractiveness. She has all the personality and charm of a blow-up doll, but with less intelligence.
I have never listened much to Beyonce, she might be a slighty more talented singer/performer than Britney, but that's not saying much. Appearance-wise she is attractive enough, but so are thousands of other wanna-be pop divas...
I am not sure what the appeal of either is. Madonna in her heyday would out-entertain both of them, by far. Even now, she totally stole the show from Britney in the video they did together.
No Apologies