If you want to gain just any mass, including fat and water retention, then obviously mass gainers would be a better choice, since they contain a lot of additives and sugars that are not needed for a healthy and lean athlete. Meanwhile, whey isolate has no carbs or fats in it, so it will only promote lean mass gains, that is - gains of higher quality. Therefore, better stick to a product made completely with whey isolate, such as the Isolation by n2bm. It has no artificial sweetners, nor additives, and it is made completely with whey isolate, which is the purest form of whey protein. Therefore, you would benefit much more and would get much healthier results with whey isolate.