In all honesty the best alternative to twitter is no twitter, until we find a better format for community discussion. Maybe it's private community chat, or similar, not sure. Maybe it's the end of public social. I think a lot of us are just looking for quieter smaller groups to share with.
A note on Mastodon. It's going closer in that direction of community specific servers but I think a better alternative would be if we could keep it private and cap group sizes. Right now it just feels like a replica of twitter segregated by topic or community. All the inherit bad behaviour still propagates because of the form factor.