Bluesky is neither decentralised nor federated.

I wouldn't let that stop you from signing up for bluesky -- in my experience it is definitely the best of the options for a twitter alternative -- but you should know exactly what it is you're getting into before you get into it.

And if you want to know exactly what you're getting into with bluesky, you should read this, which tells you more than you really want to know: https://dustycloud.org/blog/how-decentralized-is-bluesky/

I think a big pro for Bluesky from a tech perspective is how widely people are using their own websites as their handles and as verification. It doesn't do anything to protect Bluesky from going to hell but it does make it significantly easier to relink with people again.

Mastodon has failed to show any signs of hitting a critical mass so I kind of feel like it's a different level of social network altogether. A lot more durable and worth making an effort with but unlikely to ever become much more significant than it currently is.

Twitter is valuable only because of its network effect. Not everyone is going to try both of the apps. Thus, they will lag in both places.

There can be only one winner I presume.