Anyone has insights on which of these networks really have gained a strong, stable user base? I hear a lot on mastodon for instance, is it really becoming bigger or staying very niche?
If you’re plugged into one or two of those communities Mastodon will absolutely replace Twitter for you. If your community isn’t strongly represented, it can feel dead. You need to follow more people on Mastodon than you would elsewhere to get a good experience, and discovering those people can be hard.
Bluesky: 1M+ downloads
Mastodon (official client): 1M+ downloads (there are multiple clients but most downloaded one is probably the official client)
Threads: 100M+ downloads
As a user of Mastodon and Threads, I feel like Threads has the most active user base and also it is possible to find more popular or official Twitter users on Threads as well. The biggest lacking features are trending topics and DMs. Also the video player features are annoyingly lacking, can't even pause a video on web player. If they can implement these features quickly I think it is a viable alternative to Twitter/X.
I recently got invitation for Bluesky and briefly tried it, but unlike Threads, I couldn't find anybody who I was following on Twitter. Also it was a bit hard to discover new people, so I just left.
I'm not convinced that there will be one replacement-Twitter; historically with dying social networks that usually doesn't happen. Livejournal people mostly didn't flee to Dreamwidth (the Livejournal clone), say; they went to Tumblr or twitter or various other rather dissimilar social networks. I think Digg->Reddit is possibly the _only_ major example of a drop-in replacement working out.