Ok, first of all, the types of protein doesnt change whether one is off or on. You should always strive for high quality protein sources and the only time when type matters is time of day, etc. Such as a fast digesting powder after a workout and a slow casien before bed. The only thing that should really change is the amount on and off. Usually 1.5 gms per pound off is good, and 2 gms/lb when on is a good rule but different people respond to more or less. Lastly, protein is not protein. Soy is does not even come close to whey and casien digests differently than whey etc. As far of what type of powder i would go with a hydrolized whey protein if you can afford it