I like the fact that Bluesky is topic-agnostic, unlike a lot of the Mastodon instances which are organized by community (except some large ones such as mastodon.social). I always felt awkward of having to commit to a specific community upfront when signing up.

Some might argue that Mastodon lets you follow users on other instances, but my experience is that the federation depends on agreement between the instance operators, and it didn't work for the two instances I was using (mastodon.social and doll.social). It's also unclear if posting things that are off-topic to a particular instance is good etiquette.

Better moderation and account migration come to mind.