On dogfoodanalysis.com the top rated foods (6 star) have breakdowns in the range of
Crude Protein, min. 34 to 42.0%
Crude Fat, min. 16 to 22.0%
Crude Fiber, max. 2 to 6.5%
Of course the ingredients that make up the nutrients are very important. The protein should come from meat and not beans. The fat should be animal fat and not vegetable fat. The fiber should be nutrient-dense veggies, berries or grains and not some pulp by-product (ie. sugar beet pulp).
Depends on the dog as well. Dogs don't require carbs but may need them for calories, Sassy did. Dogs need fat for energy and good skin/coat health but may not tolerate much, Sassy could only tolerate something like 15% fat. The rest is best as protein to build strong lean muscle mass. Sassy was far stronger on 29% protein than 21% and Max is far stronger on 50% than 21% protein.