If you currently have a body fat percentage greater than 15% as a man or greater than 20% as a woman and your primary goal is to lose weight and body fat, most reasonable diets will be effective in helping you achieve this goal. I personally believe a ketogenic diet is the most optimal because it acts as a natural appetite suppressant and, for me, the food options are far easier to stick to than other diets. At these levels, finding a diet plan you can actually stick to is the most important principle.
However, if you are an athlete, bodybuilder, or plan on training with weights during the diet, the advantages of a ketogenic diet become much greater. By correctly applying an advanced keto diet variation, it becomes possible to maintain or even gain strength and muscle mass while losing body fat even for people in the low ranges. I suggest that everyone who truly wants to improve their overall body composition work towards applying one of the advanced systems. Even if your body fat is currently in the higher range, weight training can make a massive difference in how you look as you lose weight. Everyone who is lifting in the gym or doing intense cardio workouts should apply one of these advanced keto diet variations for optimal results.
The two effective advanced structures of ketogenic diets are the:
I strongly prefer CKD as it maintains a traditional ketogenic diet for most of the week, but allows a 24-30 hour carb-up period each weekend. I find this quite easy to structure within my schedule and, in general, this diet is usually optimal for bodybuilders.
However, if you are an athlete such as a runner or cyclist that requires training for intense periods of cardio, TKD may be optimal for you since it allows structured periods of carbohydrate intake around each workout.