Object or extend prototype

Re below snippets, can anyone advise what is least expensive from a memory perspect. I have a habit of doing the former, since I thought I had read it saved memory (or at least was quicker??) but notice that many of the modules extend prototype. So which is better, this?

var myObj = {
 myproperties: {},
 method1: function() {},
 method2:function(){}
};

or this?

myObj = function(){
 this.properties = {};
};
myObj.prototype.method1 = function(){};
myObj.prototype.method2 = function(){};