Britney and Xtina were bigger. They were the only pop girls in that bubblegum scene that people actually cared about. Everything else was ran by the boy bands. Nobody gave a damn about Mandy or Jessica & The Spice Girls were over by then
Rihanna and Gaga at least have Beyonce and Katy as formidable pop contenders. Britney and Xtina had no one f*ckin with them in 99/00/01.
Well Britney was definitely bigger at her peak, but neither Brit or Xtina were selling out stadiums at any point in their careers like Gaga and Rih are doing now, so I will say YES!