An interesting question: what is your preferred cocoa powder. I like to use cocoa powder rather than melted chocolate in my brownies. I was wondering what everyone else used?
Cooks Illustrated tested supermarket brands against the very expensive Callebaut; and the old standby Hershey’s wound up being the winner. This link has the ratings, as well as a lot of info on how cocoa is processed:
https://www.cooksillustrated.com/taste_tests/573-supermarket-cocoa-powder
I don’t have a preferred. If possible I won’t choose a Hershey but even they can’t mess up cocoa powder too much.