Which type of whey protein is the best for muscle building?

Grass fed, low temp.: I advise whey protein from grass-fed cows not given hormones or antibiotics & processed at low temperature to preserve immunoglobulins & other beneficial components. One brand that meets this criteria is whey cool by designs for health. I can't say for sure it is "the best" but it is the best i know. See http://www.Rockwellnutrition.Com/p-designs-for-health-whey-cool-vanilla-organic-whey-protein.