There is no one *best* food. There are many good ones. Just about anything is better than Puppy Chow, so you are on the right track.
Is PetCo your only option? If so Natural Balance Ultra Premium is a good food. Otherwise try these websites to see if you have a store near you that carries one:
www.canidae.com www.naturapet.com www.merrickpetcare.com www.innova.com http://www.oldmotherhubbard.com/dogs..._overview.html http://www.solidgoldhealth.com/