Reddit: decent with reports, they often act (on certain report types) and give you an update when something is done
Facebook/Instagram: most of the time there's no reply, and when there is a reply it's "doesn't violate anything". Only once or twice did I get something removed, and it was a stuff like direct threats to another user in the comment section
Google/YouTube: Never hear back about anything. The reports go straight into a trashcan for all I know