I have a campaign that has been part of a client's account I manage. They are splitting into two companies, and I want to take the campaign that applies to the new company and move it. Do I need to start from scratch or can I move it out of one into another from MCC?
You want to make sure that you don't lose any quality score that you've built up. Transfering using the AdWords Editor will lose that quality score.
If you speak to Google, they should be able to transfer the campaign for you while keeping the quality score. They'll probably need an email from the named account holder confirming what you want to do.