Singers who've hosted 'Saturday Night Live': Grading their comedy skills

When Justin Bieber hosts this week's "Saturday Night Live," he'll join a long list of singers who have shown off their comedy chops on the late-night sketch show.

It's a natural fit -- musicians are born performers. But some singers have turned out to be funnier than others in the "SNL" spotlight. We graded some recent hosting efforts:

Adam Levine: D+

Levine was definitely game (and gets the plus for taking off his shirt), but he had trouble reading the cue cards, and his energy wilted toward the end of the show.

Bruno Mars: B

Visibly nervous at first, Mars calmed down and produced some laugh-out-loud moments.

Mick Jagger: A

The veteran Rolling Stones frontman proved he knows how to work an audience. He brought the swag.

Katy Perry: B-

Her impersonation of Florence and the Machine was killer, but the show could've utilized her more.

Justin Timberlake: A+

He can do no wrong on "SNL," from his hilarious appearances in digital shorts to his monologue -- one of the best the show has seen in the past few years.

Elton John: C

It's a little hard to grade the crooner because he was constantly upstaged by cameos from Tom Hanks and others.

Miley Cyrus: C-

The writing did her a disservice, as Cyrus was made to sing in almost every sketch. Lame and predictable!

Taylor Swift: A

After a funny, self-deprecating monologue, Swift showed off a knack for spot-on impressions (her Shakira was scary-good).

Tell us: Which singers have done the best job hosting "SNL"?