How do you efficiently store data about a game?

What is the best way to go about storing a bunch of data about a game?

Let's say that I wanted to make a RPG game with a bunch of quests and weapons, armor, tools (you get me) and I wanted to make sure it all saves and loads properly.

Would you just use JSON and decode and encode the string or just have a complex table like:

local data = {
    armor = {
        gold = false;
        leather = true;
        diamond = false;
    },

    stats = {
        level = 20;
        xp = 1332;
        strength = 2938;
    }
};

And how would you update the table value easily without having to copy and paste the table and set each value to the previous value from UpdateAsync (gold = prev.armor.gold)