Britney Spears' breakthrough to the music scene is unparalleled. She has the record for the best-selling debut album of all time WORLDWIDE. She became an instant household names with hits like ...Baby One More Time, (You Drive Me) Crazy and Born to Make You Happy. Her follow up albums, although showed a big decline in sales, were still bonafide hist, sold truckloads of copies, and spawned a lot of international #1 hits. Britney also shook the world with jaw-dropping and groundbreaking controversial performances, especially those of VMAs. She also released a movie, entitled Crossroads which was a minor hit.
Jennifer Lopez on the other hand also shook the music scene, with the help of, ex-husband of 90s artist of the decade Mariah Carey, thief Tommy Mottola. Her album sales were not as big as Britney but still sold great and produced hits like If You Had My Love, Waiting For Tonight, Love Don't Cost a Thing and stolen hits like Ain't It Funny and I'm Real. She is also the first female to have both her album and movie go to #1 (Wedding Planner and J.Lo). Although some of her movies were flops, she still had widely successful movies such as Maid in Manhattan and Wedding Planner (which was already mentioned earlier).
So which of the two were bigger during this time frame?