One that tastes good. To get to and maintain a healthy weight, one must have a nutritious diet that supplies the correct number of calories, and the proper amount of carbohydrates, protein, fat, vitamins, and minerals. To stay on a diet long term, a person must enjoy eating the foods, or quickly learn to like them. Otherwise, one might quit the diet too easily. It is good to cater a diet to one's individual tastes.
Yes 80/20 diet. Where 80% of your diet consists of low carb, high lean protein and plant or fish based fat and no alcohol and 20% is rather unhealthy, meaning higher carb diet. If one can follow that (and I have many patients who are on it for maintenance) for most part, they can maintain their weight. So about 2 meals and 1 snack healthy and 1 meal is considered the "guilty pleasure".