Mastodon was my first experience of the Fediverse, and I forget which instance I joined. The one I chose chose was nearly empty and it felt like the only active user on there was the server admin. Abandoned it when I saw that the ‘Federated’ feed was completely filled with bots that reposted hentai from Reddit and various imageboards.
I’ve been looking for a Reddit alternative for a while now, but the ones I used before either died due to lack of users (i.e. Snapzu, Hubski and Syzitus) or got astroturfed into ultra white-supremacist cesspools (i.e. Voat and Ruqqus.)
Lemmy improved massively thanks to the Reddit exodus and apps like Boost and Sync being developed. Frankly I hope it doesn’t become mainstream because Reddit went to shit when everybody and their mother was using it.