A little over a year ago, we used a service called Open X on TuDiabetes.org and EsTuDiabetes.org, to serve our ads until we found ourselves talking to nobody when faced with a tech issue that resulted in no ads getting served. At that point, I decided to try Google Ad Manager, a free service that does the same thing (help you manage ads) as a hosted service by Google.
More than a year later (now it's called DFP Small Business, but it is essentially the same service), we continue to be very happy with the platform. It lets you manage multiple orders for multiple clients over multiple inventory locations. This is ideal for us, having two networks to manage ads on and typically having multiple campaigns under way.
The ability to manage an order includes start and end times, % of impressions and targeting by geography, language, browser, domains and much more. Also, their reporting capabilities are as solid as the rest of the Google products you may be used to, which is advantageous to you and to your clients.
All in all, DFP has become a solution that seems to meet all our needs and has been reliable in its delivery of ads since we adopted it.