excalibur is a pretty good na population. it was created from 3 of the smaller servers so i would imagine more new player friendly(this is just a guess and not factual). i haven't been on the other servers so i don't know if they are, but i know each of the others were a large server and a smaller one merged.

balmung as mentioned above has the people from the rp server on there. i don't know if you are into rp or not, but if you are that would be the server for you.

ragnarok is the european time zone server so it is a smaller server, but if you are from that side of the world it may be another you can look into.