According to Mediatraffic´s WW chart, Britney is the biggest in the hits department. Even Work Bitch was a Top 10 thanks to it´s frontloaded debut week
But in the memorability department, i guess it is kind of a tie between them all:
Britney: BOMT, Oops, Slave, Toxic, Everytime, Gimme More
Beyoncé: Crazy In Love, Irreplaceable, Beautiful Liar, If I Were A Boy, Single Ladies, Halo.
Xtina: Come On Over, Lady Marmalade, Dirrty, Beautiful, Aint No Other Man, Hurt.
P!nk: Lady Marmalade, Get The Party Started, Stupid Girls, So What.
HIAM, TTWE, Try, JGMAR and Say Something are too new to be called memorable