Britney Spears is the only answer!

Overall: Britney Spears

However, during Teenage Dream, Katy Perry was absolutely huge, and she has lots of #1's

Britney

Britney ??

I can't tell if the question asked is for real or just a Katy shade

Britney's peak has been way bigger than Katy's. And one of them has sold more than 100M albums lol

Neither sold 100 million albums. Why lying about that?

The album artist

Of course Britney sold more albums since she debuted in 1998. At the time, a lot of albums were selling as much as she did.

All I know is Katy keeps outselling her again and again since 2008.

'Femme Fatale' (2011) 1,9 million
'Britney Jean' (2013) 600.000

Albums artist

both are great but

Katy's Discography >>> Britney's

Yeah, comparing someone's 1st era to someone's 6th is completely fair. Bravo!

And using 1998 numbers for albums is fair too, right?

Too bad Britney didn't neither.

If everyone was selling the same, why is she the best selling female of her generation?

OT: Britney. But Britney is one of the biggest female artists ever, so this comparison isn't fair.. compare Katy to someone from her own generation, like Rihanna or Lady Gaga! That would be more interesting and fair

Well, the same goes for singles sales.

She didn't do promotion, didn't put out 8 videos, didn't put out a movie and didn't put out a re-release

All I know is a lot of albums went Diamond back then.
And she peaked really fast. Her peak lasted like 3-4 years?

Too bad PRISM did like 7 times Britney Jean's score without all of that I guess?

That's not a lie. Britney has sold around 88M with her 8 studio albums, and around 14M with the other albums (Remixes, Greatest Hits, etc...).