>Amazon

Guarantee you these are lots of bootlegs and other-region copies behind resold. So probably Amazon is worst for the artists because even the labels are getting cheated there.

>Bandcamp

As I understand it, this is (was?) one of the few places an artist could still get a good deal. Bandcamp positions itself more as a marketplace and takes (iirc) 16ish percent. Let me check that against their website:

"when a fan buys something on Bandcamp, an average of 82% of the money goes to you" (https://bandcamp.com/artists?from=footer)

So yeah, they get a lot of the niche weird music. I buy a lot of NWOTHM music off there for this reason.