Ooh that's tough. They were both HUGE. I'd say Britney because she sustained it for longer, and her breakdown was bigger than Geri leaving, the group disbanding, the group getting back together, the Olympics and Posh & Becks in general, cause the whole "Posh & Becks" thing is kind of local, whereas the group itself was massive and so global.
The Spice Girls were literally my life back then.
But...Britney was the one who saved my life and got me off life support when Geri almost killed me by leaving so I'm gonna say- Britney
Well, from my personal experience it was definitely the Spice Girls. I remember that my cousins and I would each be one of the Spice Girls from the movie.
It's weird how they got to even us because my family never listens to pop, we completely skipped over BOMT. Somehow the S Girls penetrated our barrier.
Britney AND the Spice Girls are hugely iconic and were phenomenoms at their peak, the world was literally at their feet. Everyone knows them, even after all these years.
But Britney is even more because of her longevity as a pop icon / legend.
Britney