You probably want to refer to this thread:
https://us.forums.blizzard.com/en/wow/t/wow-classic-era-realm-connections-coming-may-18/963728
And if you’re coming to NA Mankrik, Whitemane, and Faerlina are the normal picks.
For Hardcore play you’ll want to join Bloodsail or check out the post from Daddysinpie.
https://us.forums.blizzard.com/en/wow/t/a-new-hardcore-community/1530538