For the North American launch, we have opened several game servers.
All game servers are physically located in the USA, but their location and time zone differs, time zones being PST, EST, or CST (Luda only).

Luda is a non-PK server, meaning you can't get attacked in the open world or Cloud Crater, while such fights may happen on other servers.

It is best you choose the server the closer to your location, the shorter distance will usually mean less latency/ping and an overall better game experience.
You should also consider the time zone based on your personal schedule, typically all the evening events will usually be held between 7PM to 10PM server time, with some events at lunch as well.

Note that the servers are on Standard Time, as such the time will never change to follow Daylight Saving used in some countries.