I don't think he was picking the "best rappers". Biggie/Tupac/Nas/Rakim > Drake/Kendrick/Meek. This is a pretty indicative of the popular modern rappers, excluding Lil Wayne.
What's with the downvotes? As a big fan of Biggie I'd like to know what it means to say he's the best rapper. Lyric-wise? Entertainment-wise? Intellectual-wise?
I don't know if best is the right word, but he is definitely one of the best. Some of the things I think really make him stand out are his storytelling, his flow, and his charisma (that he looks unconventional also probably plays into this). Also Puff Daddy was instrumental as a hype man in getting him to platforms like MTV etc. And his untimely death definitely plays into the modern mythology. But I think if there is anything that truly encompasses his talent it's this video right here: https://www.youtube.com/watch?v=4hbwdAOogBw and this demo: https://www.youtube.com/watch?v=rEaPDNgUPLE&feature=kp
1. of the most excellent, effective, or desirable type or quality.
best for the most part won't mean different things to different people, but which rapper whom people think is the best is certainly a subjective thing.