Since you've got a few cockerels, as well as pullets, stick with a grower type feed. The extra calcium that layer feed has will eventually cause the kidneys to fail in those non-laying birds.
With out knowing exactly which feeds your referring to and a ingredients list it is going to say which is better than the other.
Now if your talking about Rural King Country Road Chick Starter linked below then I would have to say its a little better than the Purina feed. That is if your talking about the regular Purina Chick Starter.