I went through my mp3 folder, not much female singers there, but nevertheless, my clear winner would be (drumroll):
Category "I like it rough (but not too hardcore)":
Brody Dalle from the Distillers.
Honorable mention: Courtney Love / Hole
Category "I can also be posh":
Natalie Dessay (classical singer, i love her "Der Hölle Rache kocht in meinem Herzen")
And in the category "I like it, but I won't listen to it all day long":
the Morning Musume (the 4 or 5 first generations)
Honorable mention: Ai Otsuka