Every server is available to all regions in the world. However, there are "unofficial" server types. For example, Balmung is the unofficial role play server. So people who want to RP tend to gravitate towards Balmung. I believe there's also an unofficial Aussie server, although which one it is escapes me at the moment.

I'm afraid I'll have to defer to others that know more about the servers than me. All I can suggest is to choose a well populated server to increase your chances of finding others that play around the same time. Hopefully someone else can offer better advice than that.