based on what should I know what is the ideal weight for me to fight? , I remember when i used to be 70kg I used to look big and now i'm 82kg and I feel I'm lean i'm 18 and 181cm + 82kg what is the best weight for me?
Your best weight is the lightest you can be without affecting your endurance, speed, and ability to generate maximum power. There is no one size fit all. You height is irrelevant - it is your body type that is important. Have you been keeping a log of your physical fitness? Have you been tracking your physical strength, endurance, etc., crossed indexed to your weight? You cannot know what is best without knowing what has NOT been best for you.
The real reason why people lose or gai weight to compete in a different weight class is that the coaches believe you are better suited to compete against the talent in that class. If better talent is in you current weight class they will move you up or down based upon if your skill is better than or at least comparable to the talent in a different weight class. In high school wrestling coaches also have athlete change weight class because if the same reason and or hey have a fighter in that class and need someone in a different class in order to attempt to win a state title. You spread your athletes across the board to earn points in hopes of getting enough points to get a title. Therefore it is not about which class you will perform better in. It is which weigh class will you have the most success against because you have more skill than they do.
Probably put on some muscle which is heavier than fat. If you feel good and feel that you perform well at that weight I wouldn't change anything. If you try to lose weight you will also inevitably also lose muscle which can affect your performance.
