What is the best puppy food.... meaning less waste coming from my puppies???

I have 2 german shepherd puppies... and they currently eat Purina Pro Plan Puppy... Chicken and Rice... Im looking for a puppy food that will give them all they need and not just go right thru them... although they are growing rapidly.. I still believe that there may be a better food that will stay with them and not cause them to poop 3 - 5 times aday. Also, how often should you change ther food, if at all. Meaning... should they have a variety to choose from... like chicken, beef, liver, etc.