I click public match and have been through them all and get an error while my brother is getting no problems!
Be specific: Xbox or PS3? PS3 servers are crap for BOII atm, I'm on Xbox so I wouldn't know if it's on or off, but if it's Xbox, make sure your NAT type is Open and when you click Public Match before you click Core or Hardcore or whatever, click X and switch the Search Preferences to "Best". That's all I can say unless you have more info.
What's the/what was the error messae you received? Unfortunately if you're not in America or England this makes the searching barely possible :/