Sorry for being nosey but are you getting your pup from a rescue? from a registered breeder? Kijiji ad? German Shepherds are known to have GI issues and be picky eaters, so I would start off with whatever the breeder is feeding for a little while even if it doesn't meet certain standards. A reputable breeder would have years of research and litters to back what type of food they use and I would go with that until at least a few months.
Other than that, if your pup comes from an adoption or ad, then I would keep it on what they're feeding for a few weeks. At least until the dog is settled, then move onto something you prefer. There are many options out there, but I do know (from my aunt a breeder of GSDs) low carb, grain free works best for them. Particularly slow rotation diets. My aunt personally used Orijen, her dogs are picky but have never had GI issues with this food, but there are many kinds out there that are fine. Go forth and ask questions!