Gaga, because she was liked by young adults and grownups along with the teens.
Britney was just a teen sensation.
If you sell as much as Britney did you have to have the general public on your side not just teens. Everybody loved Britney back then. Not just kids and teens. I remember my teachers stanning for her. It's kinda creepy now when I think about it.
Considering half the people in here weren't even alive when britney debuted they shouldn't be saying anything I've experienced both and britney had the biggest debut. She was EVERYWHERE. Now, I will say Gaga is the only pop star that came after britney to ever get close to britneys debut. She was like an 8.5 while britney was a 10.
Lady Gaga. Britney peaked higher overall though.... Britney's first album debuted with less sales than Gaga's despite being in 1999 when sales were typically much higher. However Britney's second album made her a superstar selling 1.3 million copies in a single week. Gaga is due for her In The Zone album tho...
Sales aren't a huge factor in someone's overally impact, the social impact and hype around Britney was unmatched. Gaga was big but she wasn't quite the phenomenon that Britney was, however I think in the 90s pop stars were a much bigger deal in general than today, so maybe if they had both debuted at the same time we would have a better reflection.
