Yep, she’s amazing. One of the most creative female singer-songwriters I know.
Now to my favorites: since it wasn’t specified, I’ll go ahead and interpret this as “best vocalists” in terms of enjoyment of the whole listening experience rather than them being the best in terms of pure vocal qualities. This allows me to include singer-songwriters that have produced a spectacular combination of melody, instrumentation, lyrics and vocals, even while not having the best voices in the world, in which case:
Maria Mena
One of the main two I couldn’t imagine life without the music of. A composer and singer of own-life based music, with a direct, clear, open and sincere presentation that feels like she’s melting herself into liquid music and pouring herself into you. Goosebumps-inducing, her best songs stop me cold every time.
Best albums: “Cause and Effect”, e.g.
and “Growing Pains”, e.g.
https://www.youtube.com/watch?v=r_oeXFCf-cA
but with very good tracks on the other albums too, e.g.
https://www.youtube.com/watch?v=LXAMx1gskWA
Sara Tavares
Her second and third album are pretty much the perfect positive-vibe sunny beach pure-dripping-happiness music, a blend of Portuguese-African folk (from the West-African island of Cape Verde), soul and jazz influences, with lyrics in Cape Verdean Portuguese Creole language.
https://saratavares.bandcamp.com/album/balance
https://saratavares.bandcamp.com/album/xinti