Madonna is the queen of pop and had severals peaks imo (her greatest hits (i don't remember the title lol), Ray Of Light)
Mariah is the queen of the 90s (Music Box was big).
Céline sold a lot of albums and is not only big in the US but also in Europe and especially in France (Falling Into You & D'Eux were two HUGE eras).
Britney was HUGE during BOMT and OIDIA.
Janet, as much as I love her, was not as big as the others.
Lady Gaga same as Janet but I like her less.
Mariahs peak throughout basically the whole 90s is phenomenal.
Album peak era i think its lady gaga (dont cuss me lol) Having a 15mil selling album in 2009 (and smash 10mil selling singles) >>> having a 20-30mil selling album in the 80s/90s.
Most of you are basing this only in album sales when the peak is about the music, charts, impact, media, etc. If we go by this Madonna slay them all but Mariah & Janet come after her. Janet's peak isn't bigger than Britney, let's not.
Madonna's peak has the biggest legacy
Mariah had the longest peak and with the best sales out of any female artist, I can't think of anyone with a decade long peak.