To lose fat you need to burn more calories than you consume.
ALL diets work off this theory, but they have different ways of doing so. Some examples below:
Herbalife/Shakeology/Huel - Replaces 1-2 meals a day for a low calorie shake. Less food = less calories.
Intermittent fasting (16/8, 5:2, eat-stop-eat, Warrior Diet) - You go through periods of not eating and periods of eating. All the different windows are different. 16/8 is where you only eat for 8 hours in the day. 5:2 is where you hardly eat for 2 days of the week. Eat-stop-eat is 24 hour fasts once or twice a week, Warrior Diet is eating raw fruit/veg throughout the day and one giant meal at night. They all have the common theme of skipping a meal/meals = less calories.
Low carb diets (Atkins, Keto) - Limits/eliminates carbs in the diet. Cutting out things like bread/pasta/rice/potatoes/cake = less calories
Low fat diets - Limits fats in the diet. Fat has a 9 calories per gram compared to carbs and protein, which have 4 calories per gram. So cutting out fatty meats and processed food = less calories.
High protein diets (Dukan) - Limits carbs and fats and gets majority of food from protein, having some protein only days. Cutting out 2 macro nutrients = less calories.
Paleo diet - Based on eating like a caveman, eating whole foods and avoiding processed foods. Avoiding processed foods, which are often high in calories = less calories.
Juice diet - Put fruit and veg in a juicer and replace a meal for your juice. Sometimes done as one meal replacements, sometimes done as a juice fast where all you have is juice for an extended time. Skipping a proper meal = less calories.
Weight Watchers/Slimming World - These basically are tracking calories throughout the day, just with their own methods and names. Foods low in calories are usually called "Zero Point" Foods or "Free Foods". Foods high in calories have a higher "smart point" number or are called "Syns". You're meant told how many "points" or "Syns" you're allowed to have a day. Fewer foods high in calories = less calores.
Every meal plan you will ever see for sale online is based on eating less calories.
So, which is the best?
The one that works for you.
And what works for you might not work for someone else.
How many times have you seen people try a diet and have huge success, only for you to try it and fail? That's not necessarily because the diet doesn't work, but that it doesn't work for you. If, for example you love carbs and you enter a low carb diet, you're not going to enjoy it so you won't maintain it.
Of course, feel free to experiment with various diets and if you find one that works for you, that's awesome! If it means it works for a time but then you give it up entirely and your weight keeps yo-yoing then that actually means it's not working for you so move on from it.
Another thing to consider when picking a diet is that some are cutting out entire food groups, which are actually needed for good health. So while you might lose fat, you might not be getting the nutrients required for good health.
My personal recommendation:
You already have a diet, you don't need to spend money on a new one!
You know what you enjoy eating maybe just focus on smaller portions and over time tweak your diet to incorporate all the good stuff that you need.
(Small plug: That's what my FIT Plans are all about. First step is helping you get into a calorie deficit, and every 2 weeks you're given nutrition information to teach you what and why certain foods are important for good health so you can make little tweaks and make your own diet work for your own results. Because you get to pick the foods you like and eat whenever you like, you're more likely to learn good habits for the rest of your life, rather than a diet that helped you get a quick fix. Visit my FIT Plans page for more info)