I would say
Beyonce slayed Ashantis career because she was the one with the hits and crossover appeal to pop.
Beyonce stans are the worst and doing the absolute most for including Sunshine anderson, Lil mo and other artist with no crossover appeal. Beyonce nailed Keri Hilson but that was because she was mouthing off. I don't think she would have gotten that far, though.
Britney nailed the blonde pop stars and the anti Britneys (minue Pink and Avril). There was this one chick in the mid 2000s that came out swinging against Brit but she was a nobody so...
Madonna nailed Cyndi Lauper
Janet nailed Paula Adbul
Mary J nailed Keyshia cole and whatever r&b star out for the moment
Nicki nailed Lil Kim
Britney, Beyonce, Shakira and Pink potentially nailed Christina (See my dissertation here:
http://atrl.net/forums/showthread.php?t=184010)