What is the best protein powder for muscle gain?

Best overall: Optimum Nutrition Gold Standard 100% Whey is the safest default for muscle gain because it’s widely used, easy to mix, and gives a practical whey protein dose for hitting daily protein targets.

That said, the “best” protein powder depends on your diet and stomach tolerance. For most lifters, choose a whey protein you’ll actually take consistently, then focus on total daily protein, progressive strength training, enough calories, and sleep. Protein powder helps muscle gain mainly by making it easier to reach your protein intake; it is not a muscle-building shortcut by itself.

Quick guidance: aim for roughly 1.6–2.2 g protein per kg of body weight per day if you train seriously, and use powder to fill the gap after food.