1.Etta James
2.Janis Joplin
3.Aretha Franklin

Best Female Vocalist
 

Just considering the English speaking ones, these are some of the names that come to mind.

Jazz - Ella Fitzgerald, Sarah Vaughan
Rock - Janis Joplin
Soul - Aretha Franklin
Opera - Leontyne Price
Blues - Billie Holiday
Pop - Barbara Streisand
Country - Patsy Cline

One of the best modern pop/bluesy vocalists is Amy Winehouse. She was incredibly talented.

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"The object of the superior man is truth." –Confucius
Ajay Mac - AKA A.J.

I think Mariah Carey is one of the best singers ever. She is beautiful and I like her style. She has more number one hits than any other female performer in history. Her record breaking 18 number one singles is tied for second best along side Elvis and only trails the Beatles 20 number one singles. Her voice has continued to inspire a generation of female performers which include Rihanna, Christina Aguilera, Britney Spears, and Kelly Rowland to name a few.

Mariah is definitely up there. Though I'm biased because I'm French-Canadian, but Celine Dion as well.

Ellie Goulding

Karen Carpenter or Stevie Nicks.
Ain't nobody gonna use autotune.

Among the best female vocalists, IMO, are Linda Ronstadt, Billie Holiday, Aretha Franklin, Patsy Cline, kd Lang, PJ Harvey, Bettye Lavette, Sharon Jones, Rachel & Becky Unthank, Sandy Denny, Anne Briggs, Laura Marling, Caitlin Rose, Aimee Mann, Fiona Apple, Lucinda Williams, Camille & Selda Bagcan (Turkish psych-folk).

My current favorite female vocalist is Julie Fowlis who sings in Scottish Gaelic.

The great (and vastly under-appreciated IMO) Carrie Akre

With enormous respect to so, so many women that have made popular music in my lifetime, without question my pick for the greatest female musician since the rock & roll era began