Lemm.ee best instance, lemmy.world worst instance.

It doesn’t matter how many communities an instance hosts since you can interact with any community on any instance (barring any defederation). Lemm.ee’s strength is in being a fast, reliable instance with the best admin.

It does not matter how many people are on your instance. The only things that matter are that your instance hasn’t been defederated from other instances with communities you’d want to participate in, that it is kept up to date and online, and that your instance owner/operators stay on top of moderation. I’ve not heard of any problems along these lines with lemm.ee

Learn how this all works and think about asking a different question.