Both—we recommend testing all of your dogs.
We recommend testing all dams and sires prior to breeding. Our lab can then develop a risk assessment for a litter of puppies from the test results of pairing a specific sire and dam. If the sire and/or dam is a carrier or at risk for a particular condition, we recommend testing the puppies as a portion of them could be at risk or carriers themselves.
The statistical chance of a litter containing carrier or at risk puppies can easily be calculated based on the parents' genotypes. You can learn more about the benefits of litter testing here: Bring the Family: Why You Should DNA Test Your Litters