Eagle Pack is definitely higher quality than Royal Canin (not only the Size Nutrition, but also products like Sensible Choice, Natural Blend and Excel. The two low-end products, Kasco and Wayne, don't even fall into the same group though. Eagle's"budget" Prism line is better than those though. ).
Check out their information on ingredients, like for example antibiotic-free chicken and duck meal, lamb meal from free-range, grass-fed sheep, species-specific fish meals, non-GMO corn, quinoa, and oatmeal, no soy oil, no rice hulls etc., and better quality supplements.