Q: What is the best brand of chicken feed?
A: That's a little like asking for the best brand of jeans. In other words, most major brands are going to be fine, and what's "best" will depend on you and your needs. It will be a matter of what is convenient to purchase, what the cost is, and maybe a matter of how well something "fits" your flock and your family. If you want organic, non-GMO feed, a regular feed just won't be a good fit for you. Some flocks prefer pellets; others prefer mash. Some breeds convert feed efficiently and can do with less protein, while others may need more.
If you switch feed to test out a different type, just be sure to do so gradually... and keep notes. How do they do? You may be able to eventually nail down the feed that works best for your flock.