There is a big difference. Myoplex is categorized as a Meal Replacement Powder, comprised of protein, carbs, vitamins and minerals – 280 cal, 3 g fat, 23 g carbs, 42 g of protein…the whey protein is made to specifically supplement your protein intake – 120 cal, Fat 1g, Total Carbohydrate 4g, Protein 24g. I think you should consider your goals. If you are looking to build and gain size and strength, I would suggest Myoplex as fourth and fifth meal. If you are on a cutting phase, then go with only the protein. Either way, your body will go into a phase of fasting when you sleep. Regardless of your goal, a great way to not waste the protein AND help your progress would be to use one serving of the protein just before you go to bed. Good luck with your training!