I wanted to second Spencer's comment about the Purina. My vet said that he had never fed his pets anything but Purina products and that they are fine.
Of course, I'm going to a little extra expense and feeding mine BilJac Select, which I can get in large bags at Petsmart. Mimi is so thin that I thought she could use the extra nutrition, and she likes it a lot. Before we got Butter (or Butter got us), Mimi was eating Purina Kitten Chow all the time, for the extra nutrition, even though she's almost 12 years old. Plus, they get a can a day to split as well, and sometimes choose the dry over the can anyway.