I didn’t realize this until I started self-hosting my own instance, but if you don’t join one of the 3 large instances (beehaw, world, ml) then you miss out on a LOT of historical content. The way federation works is that it only pulls in new post/comments after someone on your instance subscribes to a community on another instance. So if you find a cool new community on another instance, you can subscribe to see any new posts and comments, but you won’t see any of the old content at all unless you manually search for the post/comment.
Long winded way of saying, the best user experience (content wise) is always going to be on the largest instances unless Lemmy/ActivityPub changes how content backfilling works.