In all honesty, pop. It's pop by a far margin. Hip hop and rap became pop under many artists. Lil Wayne isn't a rapper, he's a pop artist, same as Kanye West. Rock became pop with alot of the garage sound bands. The "emo" and "punk" groups became pop. And of course acts like Justin Timberlake, Avri Lavegne, Hannah Montanna, The Jonas Brothers and so forth so more albums than any rappers or rockers or punks or country boys. MTV, once the outlet for buzz bands and diamonds in the rough became a pop station. Pop music from Soulja Boy to Fallout Boy dominated the decade. The 2000's are the pop decade more than any decade since the 50's. Not only did rap influence fashion, so did the faggy "Emo" bands with all these youngsters wearing those tight jeans and stupid snow caps and whatever the flavor of the month was, which was usually a pop phenomenon, and MTV had alot to do with it. In the 80's the video killed the radio star, and in the 2000's MTV killed independent thought in music.