Pick a Launch Server if you're starting fresh and want a level start. Pick an Early Access Server only if your friends are already on one, because NC says Early Access players will only be able to transfer between Early Access Servers, not to Launch Servers.
That makes your first server the hardest choice in Aion 2 to undo, since it also sets your faction and your Market. Everything below comes from NC's official notices, checked on 13 Oct.
As of 13 Oct there are 104 servers. Names repeat across regions, but each is a separate server. Elyos first, then Asmodian:
A lot of Aion 2 doesn't care where you land:
