JavaScript でカスタム オブジェクトを作成する場合、プロトタイピングとクロージャのどちらを選択するか?

function Shape(x, y) {
  this.x = x;
  this.y = y;
}

Shape.prototype.toString = function() {
  return 'Shape at ' + this.x + ', ' + this.y;
};

function Circle(x, y, r) {
  Shape.call(this, x, y); // Invoke base constructor
  this.r = r;
}

Circle.prototype = new Shape(); // Inherit prototype

Circle.prototype.toString = function() {
  return 'Circular ' + Shape.prototype.toString.call(this) + ' with radius ' + this.r;
};

function Shape(x, y) {
  var that = this;

  this.x = x;
  this.y = y;

  this.toString = function() {
    return 'Shape at ' + that.x + ', ' + that.y;
  };
}

function Circle(x, y, r) {
  var that = this;

  Shape.call(this, x, y);
  this.r = r;

  var _baseToString = this.toString;
  this.toString = function() {
    return 'Circular ' + _baseToString.call(that) + ' with radius ' + that.r;
  };
};

var mycircle = new Circle();