Lauryn Hill easy for me. If I can only hear one voice sing/rap is definitely going to be a female. Her content has to be the deepest from a worldwide superstar..after Pac...and her taken rivals any male star. Her music is soulful, relaxing , refreshing and enlightening. Something you can listen to everyday and feel good, not a bunch of songs about money, dope or nikkas simp singing to women.
I didn't think of Pac though

.....he'd be a close second