My answer is always the same: do some research so you can make an informed choice for yourself and your pets. A good place to start is here.
Personally, I feel best when I keep it simple and have the most control over individual ingredients. For me, that means shopping at my local health food store and home-cooking from scratch, 2-3 organic, all-natural ingredients (organic, free-range ground turkey, organic quinoa and/or millet, grated raw veggies) and adding a few very high quality, clean (no additives, fillers, or flavorings) supplements (I've had great success with Azmira Sea Supreme and Mega-pet Daily).
Please take the time to be informed about what your pet is consuming so they don't end up being a bag full of chemicals. Remember, even processed food labeled "all natural" can be deceiving. In addition, every consequent treatment hinges on the foundation built by diet as well-respected herbalist, Michael Tierra reminds us,
"Diet is the essential key to all successful healing. Without a proper balanced diet, the effectiveness of herbal treatment is very limited. With the appropriate eliminative or balanced diet, herbal treatment will prove itself to be effective where no medicine will work and will often be faster than the quick but temporary relief of Western drugs."