Bsky’s pros:

• Some more influential/popular, and creative people have joined.
• Full account migration across instances.
• Initially at least: lower population/exclusivity, meaning less noise and fewer personality clashes, fewer trolls, so “better vibes”.
• More focused interfaces providing smoother user experience.

Somewhere in-between:

• More social algorithm friendly, i.e. feeds with posts from what your followed accounts are liking or commenting on.
• Quote posting (this one I’m counting as in-between because some Mastodon people really dislike them).
• Full text search by default (see second point as to why I have this here.*)

Bsky’s negatives (as of writing):

• Fewer people overall, so can seem dead.
• Some report phone number requirement for sign-up.
• No post editing.
• No video/gif posting.
• No audio posts.
• No direct/private/mentioned only messages.

*-Note: Mastodon now has a form of full text search but it must enabled by instance admins and one must opt their account’s posts into search visibility for them to show up. This is the result of the years of back & forth over the feature and is an interesting compromise approach.

Bsky/Bluesky’s tentative benefits:

• Full account migration across instances (Personal Data Servers).
• Personal Data Servers may have lower resource costs compared to Mastodon instances, enabling more self-hosting.
• The underlying protocol (Authorized Transfer Protocol/ATProto) enables custom feeds to help one find what they want to see and only view that.
• As this post details, it may enable more distributed moderation so that your host/instance isn’t necessarily the final say in what you can see.

Tentative negatives:

• Relays may have higher resource costs, reducing how decentralized/distributed it is.
• Currently Bsky’s federation/decentralization is only with self-hosted Personal Data Servers, while so far as I’m aware, they’re still operating the only Relay.
• While the protocol may enable distributed moderation, this may also be viewed as a downside as it increases complexity in regards to which moderation services/moderators to subscribe to, who to report anything to, etc.
• Custom feeds may also create a similar problem as distributed moderation in terms of choice paralysis/confusion, and further entrenching people into echo chambers more than existing social media arguably already enables.

Worth noting when compared to Mastodon:

• Mastodon has partial account migration.
• Mastodon allows post editing, video/gif/audio posts, and direct/mentioned only messages.
• Each instance’s local feed, and even its federated feed, may be viewed as providing a sort of custom feed produced by those on the instance.
• Probably closer to what Bluesky means: Mastodon also allows one to make lists of others to create a distinct feed, follow hashtags, and one may pin a hashtag in a column then add others to include/exclude to create a custom hashtag feed in the advanced web interface.
• Also although it’s clunkier in Mastodon, one may export their lists, block/mute lists, and share these with others to import to their own account.
• Bluesky also talks about different AppViews, which I think may be understood in relation to some of the different web interfaces, or apps one may use with Mastodon (one may understand this on Lemmy in a similar way, e.g. Alexandrite/Voyager~Thunder, etc.).