Hi porcupinetree. How old is the GSD you are getting. If it is just a young puppy you must of course use only a puppy food and they are on that until they are 18 months old. This is essential to ensure they get the right nutrition for their growing bones.
If it is older than 18 months the type of food depends on it's physical condition, body weight and age.
My puppy is fed on
Bosch pet food which is imported into NZ by my puppies breeder. It is not available in the shops but they deliver it to you. Take a look at their website.
Eukanuba, Hill's Science Diet, Nutrience and Proplan are also excellent foods. All of them have customer loyalty cards but they are more expensive then the Bosch, so do your sums on that. The cheaper foods at the supermarket are not really the best, it is a bit like raising your kids on a diet of McDonalds.