Join them all, for now. I think Lemmy desperately needs a mechanism for “meta communities” or something so you can view a merged feed of say “gaming@everywhere” instead of separately seeing “gaming@beehaw” versus “gaming@lemmyworld” …
For now while the fediverse is growing I'd subscribe to all of them or at least the ones with a substantial user base, to see where the majority of the community ends up.
Otherwise I wouldn't sweat it. If there's content you miss in one community then just sub as you see fit :)