The main difference between the two products is that the Advanced Recovery Formula contains both protein AND carbohydrates. This is ideal for post-workout nutrition because both carbs and protein play an important role in muscle recovery. The added carbs also add more calories to this product which will help with building mass.
In terms of when to use each: we recommend taking the ARF post-workout and the Whey Protein anytime during the day as part of a healthy source of protein in your diet. For example, starting your day with a scoop of whey in a smoothie would make a great tasting and healthy breakfast shake.