I have been using the same Mastodon instance (server) all the time, since I started using it a couple of years ago, and I haven't felt the need to switch at the moment, so I'm afraid I can't tell. I'm curious about setting up my own instance, though, but I haven't found the time to play around with it, yet.

About Nostr, I thing both (LOL). I mean, it seems to be working, but it also seems to be a bunch of different protocols and quite experimental. I learnt about it a few days ago when I posted here about Mastodon as "the" alternative to the freaking blue bird thingy, and somebody replied with "Nostr > Mastodon", which I interpreted as "Nostr is superior to Mastodon". Although I don't quite understand it very well yet, I think I'm going to love it when I do.

I've been kind of successful (at various levels) loging in at a few different sites already, like https://astral.ninja/, https://coracle.social/, or https://alphaama.com/, and some very different "things" like https://anigma.io/.

What's really cool about it is that you login into all those different "sites" (servers, instances, different protocols, or whatever they are) using the same pair of keys (a private one, to sign in, and a public one that identifies you) in a similar fashion to how Bitcoin key pairs work.

I can't wait to fully understand that beast and use it as it full potential, or as full as my limited brain would let me... ROTFL