Kaufman's Kona Solids soften and tighten when washed, sounds like a contradiction but it isn't. Their black is deep, pure and matte.
Moda Bella solids are the same thread count as Kona (60x60), but have a softer hand and a shinier finish. With black, that can affect the appearance of the color. To me, it looks 'hard'.
RJR Supreme Solids are my new favorite. They combine the best of Moda and Kaufman, imo.
Those are the three I have used, including black in all three.
I have no idea who makes the Amish Black that Keepsake sells (Keepsake does not make fabric), or even if it's the same maker all the time, but it's well liked for sure. In 15 years, I have never seen a bolt labeled "Amish Black" in the store, but most of the solids they carry are Hoffman Konas and RJR, with a smattering of other brands.