I run a few groups, like @fediversenews@venera.social, mostly on Friendica. It's okay, but Friendica resembles Facebook Groups more than Reddit. I also like the moderation options that Lemmy has.
Currently, I'm testing jerboa, which is an Android client for Lemmy. It's in alpha, has a few hiccups, but it's coming along nicely.
Personally, I hope the #RedditMigration spurs adoption of more Fediverse server software. And I hope Mastodon users continue to interact with Lemmy and Kbin.
All that said, as a mod of a Reddit community (r/Sizz) I somewhat regret giving Reddit all that content. They have nerve charging so much for API access!
Hopefully, we can build a better version of social media that focuses on protocols, not platforms.
I believe from Instance A, you can only subscribe to a community on instance B if both A and B allow it. Otherwise you need to create a different account in instance B.
This way an instance can have some kind of governance over its users and the content they see.
I wonder if an SSO solution exists and is supported by many instances, so as a user you won't notice much of the different accounts you could have.
At the moment I'm just using the search within Jerboa to do that. It's at the bottom of the app, and I just search for Formula 1 it will bring up a list of communities with that title.