Britney is my favorite singer...duh. But as far as singing AND songwriting goes, my favorite artist would be Mariah Carey. I don't think anyone has a voice as amazing as she does...and her writing skills are strong too.
I love Shakira too...her writing style is really unique.
BRIAN MCKNIGHT. Holy FUCK. My God...I love that man. His voice...and his lyrics...I can't even tell you how incredible I think that man is.
And of course...Pharrell Williams. He would be my favorite singer/songwriter/producer.
