In my opinion, the quality is equal. The only difference I'm aware is most WPC's sold have slighty more carbs and slighty more fat, but i doubt choosing WPC over WPI will make a noticable difference in your physique. Alot of the claims companies that sell WPI make are overstated. I think if u have a set amount of money that your gonna spend and you must spend it and cant save it... then i would still get WPC,but maybe try a product like FUZU or something else with the money that i saved from not buying WPI. The only reason i can think of to buy WPI is if your on a ketongenic diet,but your suppose to eat higher fat on those anyway and most i dont think use whey on it,or if they do very little so maybe a pound or so if u were to do that,but i dont know if whey would be the protein of choice if on that diet either, but not sure about that.. mentioning just incase.