I tried grain-free (chicken and the 6fish formulas from Orijen) but found it too rich and hard on their stomachs. I now rotate between merricks, acana and go! (the ones with grains, they do really well on the lamb formulas), with some honest kitchen dehydrated raw. I find the foods with grains much easier on their stomachs. What I look for are foods that don't have "bad" grains and not as the primary ingredient (corn, corn gluten, etc.) but better ones like barley or oatmeal, and a few ingredients down the list after some quality protein. I think it contributes to a more rounded diet and like you I supplement with fruits, vegetables, meat I cook and also give a probiotic.
Some say dogs don't need grains and that they're unhealthy- but when it comes to dog food in general people have very different opinions and can be quite passionate about it
Lady (1.5 year old tricolour) & Gracie (4 year old blenheim)
"Happiness is a warm puppy" - Charles M. Schulz