Britney by far. She completely dominated everything. Jennifer was a distant second but when you take into account Britney's musical dominance along with the media/public interest and how huge she was during her peak then it becomes apparent that Jennifer doesn't have a chance by comparison. You would be better off comparing Jennifer's peak to someone like Christina, Katy, Rihanna or Beyonce in other words someone who never truly dominated. Britney's peak was more along the lines of what Adele is now experiencing.
As someone already said, Britney may have sales but JLO in general was HUGE! She had not only multi-platinum albums but als Box Office smash, clothing line, perfurms, etc.
Overall in ALL areas JLO was a stronger force than Britney, counting fashion and movies, since Britney was only in her music niche.
