I have being in Gilgamesh, leviathan and just laterly (almost 2 months now) on sargatanas and I have seen this.
Gigamesh is great if you want to commit to the game. Make a mistake and you're fired. (see the boards, they are good at solo Rankin but not at party ones)
Leviathan is Great place, but... I didn't fit in the end. I don't know exactly what happened. May I was too busy on my own
Sargatanas is super friendly, people is more relaxed and more party friendly. They wait on new players, and tho I admit levathan and gilgamesh are more populated. Do you really need 15k payers running around to enjoy the game?