It'll probably be ActivityPub. All the other protocols are too onerous for people to understand.
AP has the simplicity of email, the potential for easy centralization (...like email, which makes it aligned with corporate interests) and is something that most users will be able to figure out. It's also very much build around the "worse is better" mindset, where the protocol has very obvious deficiencies yet people are so used to those deficiencies that it's growing in spite of those with no replacement in sight. ActivityPub will succeed for the same reason that Outlook is still the most used email client today even though everyone can agree that almost any other client is better: it's entrenched.
Nostr and Bluesky are trying to do decentralized identity, which while admirable, doesn't really align with corporate interests and it's left the federating/decentralized content parts very underdeveloped. Like, functionally speaking Bluesky is just a Twitter clone with an odd account scheme at the moment, their stuff doesn't actually federate, while Nostr has approximately zero relevance. (Bluesky at least has a userbase, even if I would personally consider it to be "the worst parts of Twitter before Elon took over". The worst of Twitter right now is well, honestly I would just say the entire site and be done with it.)