Mariah Carey, Blake Shelton, Adam Levine, Shakira, Demi Lovato, Jennifer Lopez, Nicki Minaj, Ben Folds, Christina Aguilera, Britney Spears, Usher, Keith Urban: they've all made hit records, but they've also all served as judges on music competition reality TV shows.

"American Idol," "The X Factor," "The Sing-Off" and "The Voice" have (or had) the habit of taking on chart-topping artists for their panels. While Paula Abdul and Randy Jackson helped lead the earliest charge in American reality TV, these current lineups are employing artists who are still making music -- or at least trying -- in a big way today.

But no judge is created equal. Some have excelled at being judges on their respective shows, while others have struggled. And the same goes for their music: taking on a reality television show is a gamble when trying to re-invigorate a musical career.

So, pay attention, new "Voice" judges Gwen Stefani and Pharrell Williams: in the gallery below, we give grades to show personalities, and their subsequent music careers. Who stunk and who succeeded?

After five years as a columnist and editor at Billboard, Katie Hasty joined HitFix in 2009 for music and film reporting out of New York. The Midwest native has worked as a writer, music promoter and in A&R since 1999 and performs with her band Numbers And Letters.