In a large bowl, stir together softened cream cheese, sour cream, and mayo until smooth. Fold in the shredded cheeses, caramelized onion mixture, and most of the crumbled bacon (save a little for topping).
8 ounces Cream Cheese, ½ Cup Sour Cream, ½ Cup Mayonnaise, 8 ounces shredded cheddar cheese, 8 ounces shredded mozzarella cheese