well, the natural balance LID - lamb meal and brown rice isn't grain free. I've had the boys on the Instinct LID rabbit meal, they loved it and the Fromm Beef Frittata. Currently they are on Earthborne Holistic Meadowfeast. All of Earthborne are grain free and potato free (yeast issues with potatoes). The only advice I can give is what works for one bully won't work for another so it's all trial and error. I tried the TOTW Southwest Canyon (the boar meat) and Remy started licking his paws and all the dogs had crazy gas so back to Earthborne I went. I have no yeasty paws, no tear stains, poo's are nice and firm and no gas.
And yes, you can switch flavors within the same dog food without worrying about transitioning