My musical taste is all over the board so it will definitely show when I mention my favorite female singers. But, before I dive into that I want to mention
@Wade W Wilson I like the mentions of Christina and Brody. I'm pretty sure Heaven's a lie is the first time I heard Christina, but I think my favorite song to hear her sing is "Cold Heritage". I became absolutely obsessed with hearing more of Brody the first time I heard the song "Hall of Mirrors".
But to the question at hand my all time favorite female singer is going to be Mariah Carey, I fell in love with her when my older sister brought home the "Emotions" album way back in the day. And while her recent albums and performances have left much to be desired I will never move her from number 1 in my book.
I would say my next favorite female singer is probably Nelly Furtado or Florence Welch. After them I'm a fan of Alicia Keys, Joss Stone, Pink and then Teena Marie which I inherited my joy of her from my dad. And one of my newest favorites is Noelle Scaggs from Fitz and the Tantrums.