Marty, I use both soy and whey. I have whey right now as my main protien powder, my last batch was soy. Since reading Trainerdan's book I have decided to use whey for my post workout shake and soy for my evening shake. Whey empties faster getting the much needed nutrients to your muscles, soy takes longer and is a good choice in the evening when you want to be able to feed your muscles overnight.

HTH
Nat