Easy, multiplayer. I'll probably play combat training for an hour just to get a feel of the maps, then its on to public matches. I'll play the campaign mode in little bits here and there, when i need a break or something from multi.
As for zombies, i'll play a couple rounds when im proper bored. Personally zombies doesnt have alot of replay value for me, i find it quite boring or at least i did in WaW. I might find Black Ops zombies more appealing, only time will tell lol...
A couple of rowdy games of Multiplayer with all my mates. Then say I have to go offline, appear offline on XBL and BEAST the **** out of the Campaign. Couple of levels on Veteran and then a few more Multiplayer games, this time by myself. (Probably SnD.)
Next day, I've got the day off work, so I don't know WHAT I'll do...... But you can bet it's going to heavily involve Black Ops =D
I am excited for Zombies, but it is the least of my worries, I'll play it when invited to by my friends.
Multiplayer - The first few days are always the most fun for multiplayer, because people dont camp. They all run around trying to learn the maps. Makes it more fun.