Who's the hottest young star in music? Billboard magazine says it's Justin Bieber, who edges out One Direction for the crown on the '21 Under 21: Music's Hottest Minors' list, which is heavy on teen pop acts but also features hip-hop stars like Mac Miller and country singers such as Scotty McCreery.

Bieber comes in at No. 1 for the second year in a row. The magazine writes that he "remains more powerful in the pop universe than ever... Justin Bieber is the supernova of teen pop stars with charisma, popularity and swagger to spare." In addition to his own hits, the singer helped break Carly Rae Jepsen in the U.S.

One Direction are nipping right on Bieber's heels in the reign for teen pop supremacy. The U.K. group exploded over the past year thanks to their debut album 'Up All Night.' In a sign of just how far they've come, the guys were only No. 19 on this list a year ago.

Right behind the boys is Demi Lovato at No. 3. It's almost hard to believe that such an accomplished actress, singer and new judge on 'X Factor' is still only 20 years old! 'American Idol' kingpin Scotty McCreery takes No. 4, while Pittsburgh rapper Mac Miller holds down the No. 5 spot and Bieber's girlfriend, Selena Gomez, occupies No. 6. All three acts had successful albums and singles over the past 12 months.

British pop singer Cher Lloyd takes No. 8, followed by Odd Future rapper Earl Sweatshirt and Nick Jonas rounding out the Top 10. Acts further down the list include Cody Simpson at No. 12, R&B quartet Mindless Behavior at No. 13, Miley Cyrus at No. 18 and Victoria Justice at No. 21.

Watch the Justin Bieber 'As Long as You Love Me' Video