Over the years I've tried every brand of feed I could find in my local area. DuMor poultry feed just did not give me the results I was seeing from other brands so I stopped using it. Unless things have changed Purina is the one making it, but it's not the same blend as their Purina branded feeds. My birds preferred the Purina Flock Raiser to the DuMor.
After having tried every line of feed I could find around here I now only use FRM (Flint River Mills) out of Banebridge, GA. It's a regional mill though so if you're not in their delivery zone you probably cannot get it. Of the national brands I would go with Purina.