What you need to watch for with a GSD puppy, or any large breed for that matter, is the levels of Calcium and Phosphorus (and the ratio of the two as well) in the food. Calcium and Phosphorus should be kept close to 1% and a 1:1 ratio, or as close as possible to 1:1.
Taste of the Wild, unfortunately, doesn't publish those numbers as far as I can see from their website, but they will give them to you if you email and ask about them. I emailed them quite a few years ago and remember that some of the formulas were, indeed, higher in Ca and Ph than I would be comfortable feeding, but some were acceptable. So, it really depends on the formula you are feeding ... they also may well have reformulated since I contacted them, so it would be best to email and ask about the specific formula or formulas that you plan to feed.
Also, I would definitely not recommend Purina ... even if you decide against Taste of the Wild, there are far better choices than Purina.
Omen v Wolfstraum
Jasmine Katie v Doolanshaus