It really depends, if you prefer getting to know players outside Europe, then some other server might be worth considering. And remember that you can create a team on multiple servers too, it’s just the founder’s packet that you can only get once.
EU server is obvious choice because better ping means higher dps, and the difference might be significant on those fast hitting mainly auto attack using builds. For ranged AOE builds like many mages, the ping is not quite that important as long as it’s below certain threshold, around 300ms I guess.