Welcome to the HiddenStreet community. I think you'll enjoy it here.
I'm going to assume you are a returning player - but I don't think you specifically mentioned that, so please correct me if I am wrong. I would recommend Chaos, because it is not even one month old, so you should feel more at home there with all the new players. I started in Chaos myself after being away from MapleStory for a while, and I really like the idea of every character being relatively new. I suppose there are some cons to this, even specific to new or returning players, but I feel the pros outweigh them.
Good luck, whatever you choose~