This is where it gets tricky because of demographics. Eminem sold more music to white people. White people are the majority demographic in the US, UK, and other countries. 50 Cent sold a lot to black and white people, but he'll never have or be able to draw the same amount of white fans that Eminem can. To us it feels like 50 was bigger because as a culture, black people rocked to 50's music more. But in general no, Em was bigger. Also remember that 50's music was heavily bootlegged. I think GRODT leaked 1 or 2 weeks before the release date which made the label bump the release up a few days. Still managed to sell and do crazy numbers. The massacre leaked early too and still did 1.1 million in like 4-5 days or some shyt.
In 2002 Eminem had the number 1 song, music video, album, soundtrack, and movie. Won a crazy number of awards and was the first rapper to win an Oscar. He also had the number one free agent in rap at the time who was 50 Cent. The question should actually be if Eminem was at his peak in 2000 or 2002? Cuz MMLP is what sent him over the top to begin with.