Mastodon is turning into what Twitter was and right now is likely the one out of the three to turn into the biggest echo chamber. Twitter under Elon if he keeps his promise will have free speech and no blocking. Nostr is censorship resistant. Mastodon instance admins can defederate other instsnce they do not like and turn mastodon into a echo chamber.
I think Nostr wins since as far as I know they got a blocking feature and users can choose the wild west free speech flow of information or go into a corner of Nostr and follow your interests.