Preheat oven to 375℉. Spay a 9 x 13-inch baking dish with nonstick cooking spray.
Mix the cream cheese, cheddar cheese, and Ranch dressing mix, set aside.
Place the chicken breasts on a cutting board and use a sharp knife to cut a pocket into the side of each breast, being careful not to cut through.
Divide cream cheese mixture among the chicken breasts and evenly stuff inside the pocket.
Place the chicken in the prepared baking sheet and brush heavily with buffalo sauce.
Bake for 25 minutes, brushing with additional sauce after 10 minutes.
Before serving, drizzle with additonal buffalo sauce and dressing of your choice.