So far this century, only five pop girls have released albums which have sold over 20 million copies worldwide...

Adele with 21 (28 million copies sold).



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Norah Jones with Come Away With Me (25 million copies sold).



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Amy Winehouse with Back to Black (20 million copies sold).



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Britney Spears with Oops!... I Did It Again (20 million copies sold).



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Avril Lavigne with Let Go (20 million copies sold).



...but which one is the most iconic?

Amy Winehouse with Back to Black (20 million copies sold). Avril Lavigne with Let Go (20 million copies sold).

Wow I didn't know Amy sold that much

They all sold 20 million, definitely (there are numerous sources).

Let Go was a phenomenon in case you didn't know.
Oops was coming off the success of BOMT.
And B2B reached 20m in 2012, after her death. B2B actually sold 1m+ in the week after Amy's death.

21 > Oops... > the rest