Javascript OOP and Inheritance Technique

I'm not good at English. Please understand

When my friends have javascript oop implement

function Item (a, b, c) {
    var _a = a, _b = b, _c = c;

    return {
        init: function () {
            ...
        },

        start: function () {
            ....
        }
    }
}
var item = new Item();
item.init();
item.start();

But I would like to know the following.

function Item (a, b, c) {
    this.a = a, this.b = b, this.c = c;
}

Item.prototype.init = function () {...}
Item.prototype.start = function () {...}
var item = new Item();
item.init();

item.start();

Which do you think you?