what is the most popular music in the usa
Blues, rock, R&B, gospel, heavy metal, disco, and hip hop, to name a few.
American popular music
The country has seen the rise of popular styles that have had a significant influence on global culture, including ragtime, blues, jazz, swing, rock, bluegrass, country, R&B, doo wop, gospel, soul, funk, heavy metal, punk, disco, house, techno, salsa, grunge and hip hop. 
wiki:18320422
American popular music [SEP] Introduction
American popular music has had a profound effect on music across the world. The country has seen the rise of popular styles that have had a significant influence on global culture, including ragtime, blues, jazz, swing, rock, bluegrass, country, R&B, doo wop, gospel, soul, funk, heavy metal, punk, disco, house, techno, salsa, grunge and hip hop. In addition, the American music industry is quite diverse, supporting a number of regional styles such as zydeco, klezmer and slack-key. Distinctive styles of American popular music emerged early in the 19th century, and in the 20th century the American music industry developed a series of new forms of music, using elements of blues and other genres of American folk music.