I would suggest a server with a lower population than Behemoth. I feel by Tuesday (the day the game actually launches) Behemoth will be no better off than Gilgamesh and Balmung.
As for the debate about whether or not to add a third RP server--I don't see why not? It seems like most of the people who are able to login on Gilgamesh/Balmung are against it, but then again, they are able to login. By suggesting a third server you are allowing people who are unable to get on Gilgamesh/Balmung a chance at organization. If you do not give them this opportunity then all of those locked out are just going to randomly select a server and be scattered more than necessary.
I'm not saying this is going to happen, but you do realize that Gilgamesh/Balmung might not be available for 30 days or more?