I used to use Calckey but it soon morphed into Firefish, which also didn’t last long. So, as far as stability goes: Misskey may be stable, its forks not so much. I’m currently using Catodon (catodon.social) and the only functionality missing is the antennas.

On the other hand, most of the firefish crowd migrated to Iceshrimp. You can check out the Fediverse Observer to find some english-speaking instances.