I have been hearing allot about dog food killing dogs,can anyone tell me which is the best and cheapest?

I have 2 dogs 50 pounds and above.The older 1 has been suffering from what the vets say is seasonal allergies and I refuse to put her on steroids again,so I have been looking for a good for the dog,dog food instead of hearing about most store brands that are killing our dogs everyday.I have her on Iams sensitive right now(for 2 weeks) but I am not sure if it is the dog food or the change in the weather or the med’s she was on over a month ago that is helping her.She is not digging at her paws anymore or her face and she has allot more energy again.She has also been on Acidophiles for the past 3 months(because I heard that helps yeast infections/ear infections).I have been doing allot of research on her problems for the last several months to try to help her without med’s.Can anyone give me insight on what is the best dog food or the best solution to the problem