I really wouldn't recommend an EU server if you don't wanna lose interest in the game. I've been on Cerberus for a year and people were just rude and not polite at all. On top of that, everyone kept talking in their own languages, not caring if other people would understand or not, which is pretty rude as well.

Don't join Gilgamesh or Balmung if you don't want big servers. I made friends on Siren when I was there, and it seems pretty decently sized. Lot of great folks around there