Prepare your slow cooker: Lightly grease the inside of your slow cooker insert to prevent sticking.
Combine the base: In a medium bowl, combine the softened cream cheese, buffalo sauce, ranch dressing, and blue cheese dressing (if using). Mix until smooth and well combined.
Add the chicken and cheese: Stir in the drained shredded chicken and 1 cup of the shredded cheddar cheese, along with the Monterey Jack cheese. Mix everything together until the chicken and cheese are evenly coated with the sauce mixture.
Slow cook to perfection: Transfer the mixture to the prepared slow cooker insert. Sprinkle the remaining 1/2 cup of cheddar cheese over the top.
Cook on low for 1.5 to 2 hours, or on high for 1 to 1.5 hours, stirring occasionally, until the dip is heated through and the cheese is melted and bubbly. Ensure the cream cheese is fully melted and incorporated.
Garnish and serve: Once cooked, stir the dip one last time. If desired, garnish with chopped green onions before serving. Serve hot directly from the slow cooker.