Phoinix is the most active from usa servers and Teon from euro.
But the best way to test which server u would like is make a lvl1 toon in the servers that fit your timezone(you can create toons in every server) and start going around,try to talk to people,ask for a clan academy and see where you may find friends.Most clans will pay for your toon to graduate from academy because they take clan reputation points that way.This way u will have money for better gear.Stay and lvl in a clan where you can find everyday some people around your lvl that you can play with .It's the best way to find out what class you will enjoy to play and have fun in game.