Diaspora* only supports diaspora protocol. It has about a few thousands MAU I'd say. If you use it you can interact with Diaspora* users and with Friendica/Hubzilla users from servers that have the diaspora addon. You can see a list of Diaspora* pods here.
Friendica on the other hand natively supports ActivityPub, and has addons for BlueSky, Diaspora* and Tumblr (Not all servers have them enabled). It has 3k MAU, but you can communicate with much wider range of folk. There's also the Friendica directory, allowing you to find interesting folk to follow much more easily. If you want a stable instance I can recommend https://friendica.world/ , it's managed by the admins of lemmy.world .
Let's hope that there are also a few organisations that run Friendica instances so that the offer becomes a bit bigger. In the last two years, everyone has been totally fixated on Mastodon and many have opened a Mastodon server without realising that there were other options.
I agree that it is an exceptional software, perhaps the best of the Fediverse, but it has a terrible name. The reason for this name was to mark a continuity with the first potentially federated social network, namely "identi.ca"
Moreover, despite the name, it is not a really friendly software, but presents several ergonomic complexities.
Finally, I add that when I pronounce it with my dictation system, it is always transliterated as "free handicap", which is a very inclusive thing, but every time I have to correct it... 🤣
This is also why I decided to call my instance with a different name such as Poliverso, Too bad that a few months later Zuckerberg decided to launch his failed Metaverso project, which is why every time I have to explain that I did not call it that to parody the Metaverso 🤬
I believe Facebook’s name came from an actual thing. The company was created for college students. Many campuses, would give face books that had students and professors from the universities.
Friendica was the fediverse, before there was a fediverse... And it was no different from other names of the era, like Sym.pati.co... DiGG, Reddit, etc etc.
All of those just sound easier to pronounce, even though "sympatico" is kinda longer than necessary. My point is that almost all the Fediverse software has awkward to pronounce names which doesn't really help with the initial adoption.