The fediverse (including Mastodon) is better at: having been proven to scale, having multiple places running different services, offering more choice of apps, giving a choice of legal jurisdictions and business/non-profit models, and is still growing far faster, especially globally.
Bluesky is better at: Onboarding & signup experience, having fewer choices to make, quality of the default app, familiarity for people used to Twitter's design, discovery of other users within the existing service.
@anildash My strong suspicion is that Bluesky (or any similar corporate product that preaches federation) will use federation for their initial growth spurt, and then find a way to pull up the drawbridge once private equity or the Saudis decide that lock-in sounds more profitable.
I don't know why I would be so cynical, except for my lying eyes and the entire history of Facebook, Twitter, Google, YouTube, RSS, XMPP, OpenID, and even Open Graph meta tags.