Personally I like Wellness, Core Wellness is good in general, but their Core food is grain-free and high protein and fats. My dog and cat seem to like the taste and both are happy and healthy. Wellness or similar brands may seem expensive but if you consider your GSD's long term health and fewer expensive vet visits it is worth it in the end.
More and more websites help you to make your dog food search about homemade dog food, you'll find some good recipes for your dog. best of luck