From the MAIN popgirls (Lady Gaga, Britney Spears, Katy Perry, Rihanna, Taylor Swift and Beyoncé)... definitely Beyoncé, all the other girls latest albums (including Britney Jean) are certified at least gold while Beyoncé (album) isn't.
Britney or Beyoncé, the UK doesn't really care for either of them anymore. 4 sold more than self titled while her highest charting song since 2011 peaked at #9, while Work Bitch peaked at #7 before falling to #37 the next week, and Pretty Girls peaked at #16 before falling to #55.