What is the best practice to track Agencies in your analytics reports?

I have a few agencies that I employ to run Adwords PPC and FB ads and I would like to be able to see a report where I see just once agencies performance.

Is there a way to have utm_agency or utm_customfieldname here where I can set this up? The only other way I can think of is to have all agencies start their campaigns with their name, so it would look like this: utm_campaign=agency1-campaign-name-123 and then I can filter by regex.

What's the best practice here?