A considerate question indeed, thank you. Bandcamp is the most direct source of revenue and yields the greatest share per unit sold. After that would come Burning Shed but there is a sizeable disparity between the two.
Spotify is a bit of a joke really, looking at a recent statement every $100 amounts to approximately 23,000 tracks streams. It doesn’t compare very favourably with Apple Music which is approximately double that. Still, if you’ve already purchased the music and are kind enough to use streaming sources it will count as additional revenue therefore you are entirely correct and us artists are very grateful for this type of thoughtfulness. Thank you.