For instances of mainstream Misskey:

https://misskey.de (instance by maintainers of Friendica instances libranet.de and venera.social)
I'm using misskey.social from Italy, but they have some annoying limits for new or less-followed accounts e.g. how many people can you reply to in one post (this would shut you out from some discussions...)

For Sharkey:
https://blahaj.zone by maintainers of namesake Lemmy instance
https://calckey.world or https://sharkey.world by, well, .world
https://procial.tchncs.de

For Iceshrimp: https://fedia.social (from maintainers of fedia.io and infosec.*)