Nextcloud is federated? First time I hear about that.
For me it’s Lemmy, without a doubt. Never used Twitter, tried mastodon to see what it’s all about, didn’t like it.
Matrix seems decent, but nobody I know uses it, and finding useful groups is painful, especially on other instances (servers, whatever they call them).
That was the first instance out there, so amany early adopter communities are hosted there. I’ve blocked a handful problematic users and all the communist stuff and other topics I don’t agree with or care about, but by and large it’s alright.
Hexbear.net and lemmygrad.ml are instances I’ve blocked altogether.