Lemmy.ml is hosted by the maintainers and Lemmy.world is the biggest instance (because they were one of the few that didn’t restrict sign ups when Reddit API went dark) so those users are going to have the most communities.
Despite this I still am subbed to many communities on beehaw, Lemmy.world, lemmy.ml and sh.it.just.works
And I have some subbed communities on smaller instances.
But I will say that I’m thinking of starting a new community but I’ll probably do it on Lemmy.world as they have the funds and manpower to guarantee uptime