I'm on Brynhildr and have been playing for about two months now. Though I haven't looked into it specifically, from what I've seen just going around to different places, there seems to be a good balance of people at all levels. It is one of the newer servers (but there are a lot of people on it and I see new people every day), so you shouldn't have any problem with activity being dead until end game like on some of the older ones (from what I've read of personal accounts on this forum). There are lots of free companies and most are open to people of any skill level and state of game progression. My fc of about 230 members mostly has people with at least one class at level 50 (many have several or even all at 50), but will often do lower level stuff with others if they ask, and are very helpful in general. A lot of them are west coast time zone, especially in California.

Also, I wouldn't base server activity on activity on this forum. I can't imagine most people would bother with joining here, let alone posting regularly. As active as I've seen my server, I have barely noticed anyone from it on here.

If you decide to start a character on Brynhildr, let me know and I can recommend you to join my free company once you unlock the ability to do so. The xp bonuses are nice to have, even if you aren't actively doing stuff with other members.