I think Lailah is the best server, lots of players. You can mostly find party's everywhere
But i don't know hat you mean with ''Battlefield'' You mean the PvP field, or ?
Actually, this is not true anymore. There is only one server atm, and you can get there by any of channels Lailah/Gaia/Etain/Teos. So if you choose any of these, you'll be redirected to the same server.
Regarding PvP field, there are several PvP zones: Proelium(1-15 pvp), Cantabilian(20-30 pvp), and end-game pvp (lvl 80 pvp).
- 1-15: You can get there through portal in Keolloseu (light side 1st map) or Gliter (fury side 1st map).
- 20-30: You can get there through portal in Arktuis Vill (light side 2nd map) or Starfumos Vill?? (fury side 2nd map but I am not sure about this because i've never played for fury).
- 80: There are several maps for end-game pvp, like VR, PR (invasion maps), KI, D-Water, Jungle, DD1, DD2, and some dungeons (CS, SC, D1, D2). These maps/dungeons are all accessible for every level (except KI, which is 60+), but you won't have a chance against 80s.
I hope this helps you