I stand by my contention that Craig Wedren (formerly of Shudder to Think) is the best rock vocalist alive today, having attained this status after the passing of Freddie Mercury.
Female:
Sandy Denny
Kate & Anna McGarrigle
Maddy Prior
Linda Ronstadt
Grace Slick
Male:
I don’t know.
I’ll add to the list:
Seal
Natalie Maines (The Dixie Chicks)
Elton John
Billy Joel
Female: Neko Case, Sinead O’Connor, Elisabeth Fraser (Cocteau Twins), Janis Joplin, Emmylou Harris
Male: Leonard Cohen, Tom Waits, Chris Cornell, Johnny Cash, Bon Scot, Kurt Kobain, Freddie Mercury, Elvis Presley