I'll even go one step more and defend my choices:
Judy Garland - does she even need defense? Even when her voice was shot, she could break your heart with Over the Rainbow.
Patsy Cline - she had the same emotional connection to a song that Judy had. Her singing had a ballsy-ness to it.
Billie Holiday - listen to God Bless the Child. She was drunk when she recorded that. If you can put over that song while drunk, then you are definitely a great singer.
Ella Fitzgerald - listen to Mack the Knife on her Berlin album. She forgets the words (while performing in Germany no less!!) and still goes right on with the song. She just starts scatting her heart out. And I dare you to listen to A Tiskit A Tasket and not think she is the cutest thing to come along.
Georgia Brown - her As Long As He Needs Me will break your heart. And listen to her Alabama Song -- the girl knew how to let loose.
Adele - if you can put 5 hits on the charts from just two albums, while looking like a server at The Hofbrau Haus, then you deserve to be on the list. Judy would have killed for material like "Someone Like You" which did I mention that Adele wrote?
If anyone ever tells you that you put too much Parmesan cheese on your pasta, stop talking to them. You don't need that kind of negativity in your life.