At risk of sounding like an Exhell member, Britney her rise was the biggest of any pop girl, imo.
Just because Britney was a phenomenon, sensation, and a brand with dolls, lunchboxes, appearances on very popular 90s tv shows, etc.
Madonna was putting out hits, but so were many other women (and men) in the 80s. She was never marketed as a teen pop sensation like her "counterparts" Tiffany and Debbie Gibson.
I agree. BOMT is the most massive debut single by any pop girl in history, no?