Not automatically better#
Most dogs digest moderate amounts of grains perfectly well, and grain-free isn't automatically healthier for every dog. It's most useful for the smaller number of dogs with a genuine grain sensitivity or intolerance.
Marketing around grain-free food can sometimes overstate its benefits for dogs without a specific sensitivity, so it's worth thinking about your own dog's needs rather than following a general trend.
Quality first#
Whether a food contains grains or not, the more important factors are quality protein, a short list of recognisable ingredients, and a diet that's actually complete and balanced for your dog's life stage.
If you suspect a genuine grain sensitivity, an elimination approach guided by your vet, similar to investigating other food allergies, is a more reliable way to confirm it than assuming grain-free is the answer.