Well, I originally had an account called Killbook but wanted to start fresh and made an account for Zombies and kept Killbook for my multiplayer fun. I have a family gold pack so I can have up to three accounts for a good price and I have one for multiplayer, zombies, and for my guest's.
Whatever you choose. I mainly play zombies too and play multiplayer when I'm done with a very long zombie match. Helps me get all that out of my system so that I can get off instead of playing forever.
But anyway I'll add killbook also and just in case i need a free slot I can delete normal killbook considering I can just go through zz killbooks's friend's list to get to normal killbook and vice versa.
Certified Experts is the clan I used to be in but, people kept adding the xbox account "CertifiedExperts" instead of my account and so I had to make another before I got really agervated of me posting "No, my account's not CertifiedExperts, it's Killbook".