私はお勧めします:
$('#shipping_customer_address option:last').prop('selected', true);
$('#shipping_customer_address option:last').prop('selected', true);
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<select name="shipping_address_id" id="shipping_customer_address" class="customer_address" title="" onchange="shipping.newAddress(!this.value)">
  <option value="48" selected="selected">p p, yui, cfg, 90602-1234, U.S. Minor Outlying Islands</option>
  <option value="52" selected="selected">e B, ewri, csdfwefg, 90602-1234, U.S. Minor Outlying Islands</option>
  <option value="">New Address</option>
</select>
 
 
外部JS Fiddle デモ。
または(少し速い):
$('#shipping_customer_address option').last().prop('selected',true);
$('#shipping_customer_address option').last().prop('selected',true);
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<select name="shipping_address_id" id="shipping_customer_address" class="customer_address" title="" onchange="shipping.newAddress(!this.value)">
  <option value="48" selected="selected">p p, yui, cfg, 90602-1234, U.S. Minor Outlying Islands</option>
  <option value="52" selected="selected">e B, ewri, csdfwefg, 90602-1234, U.S. Minor Outlying Islands</option>
  <option value="">New Address</option>
</select>
 
 
外部JS Fiddle デモ。
オプションvalueから属性を削除し、その属性がないことを選択するだけです。New Address
$('#shipping_customer_address option').not('[value]').prop('selected',true);
$('#shipping_customer_address option').not('[value]').prop('selected',true);
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<select name="shipping_address_id" id="shipping_customer_address" class="customer_address" title="" onchange="shipping.newAddress(!this.value)">
  <option value="48" selected="selected">p p, yui, cfg, 90602-1234, U.S. Minor Outlying Islands</option>
  <option value="52" selected="selected">e B, ewri, csdfwefg, 90602-1234, U.S. Minor Outlying Islands</option>
  <option>New Address</option>
</select>
 
 
外部JS Fiddle デモ。
または、空の属性で選択することもできます:
$('#shipping_customer_address option[value=""]').prop('selected',true);
$('#shipping_customer_address option[value=""]').prop('selected',true);
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<select name="shipping_address_id" id="shipping_customer_address" class="customer_address" title="" onchange="shipping.newAddress(!this.value)">
  <option value="48" selected="selected">p p, yui, cfg, 90602-1234, U.S. Minor Outlying Islands</option>
  <option value="52" selected="selected">e B, ewri, csdfwefg, 90602-1234, U.S. Minor Outlying Islands</option>
  <option value="">New Address</option>
</select>
 
 
外部JS Fiddle デモ。
または、プレーンな JavaScript で、最後の を選択するには<option>:
document.getElementById('shipping_customer_address').lastElementChild.selected = true;
document.getElementById('shipping_customer_address').lastElementChild.selected = true;
<select name="shipping_address_id" id="shipping_customer_address" class="customer_address" title="" onchange="shipping.newAddress(!this.value)">
  <option value="48" selected="selected">p p, yui, cfg, 90602-1234, U.S. Minor Outlying Islands</option>
  <option value="52" selected="selected">e B, ewri, csdfwefg, 90602-1234, U.S. Minor Outlying Islands</option>
  <option value="">New Address</option>
</select>
 
 
外部JS Fiddle デモ。
<option>または、 CSS セレクターを使用して最後を選択するには、次のようにしdocument.querySelector()ます。
document.querySelector('#shipping_customer_address option:last-child').selected = true;
document.querySelector('#shipping_customer_address option:last-child').selected = true;
<select name="shipping_address_id" id="shipping_customer_address" class="customer_address" title="" onchange="shipping.newAddress(!this.value)">
  <option value="48" selected="selected">p p, yui, cfg, 90602-1234, U.S. Minor Outlying Islands</option>
  <option value="52" selected="selected">e B, ewri, csdfwefg, 90602-1234, U.S. Minor Outlying Islands</option>
  <option value="">New Address</option>
</select>
 
 
外部JS Fiddle デモ。
または、認識しないブラウザの場合lastElementChild:
var options = document.getElementById('shipping_customer_address').options;
options[options.length - 1].selected = true;
var options = document.getElementById('shipping_customer_address').options;
options[options.length - 1].selected = true;
<select name="shipping_address_id" id="shipping_customer_address" class="customer_address" title="" onchange="shipping.newAddress(!this.value)">
  <option value="48" selected="selected">p p, yui, cfg, 90602-1234, U.S. Minor Outlying Islands</option>
  <option value="52" selected="selected">e B, ewri, csdfwefg, 90602-1234, U.S. Minor Outlying Islands</option>
  <option value="">New Address</option>
</select>
 
 
外部JS Fiddle デモ。
valueを使用して空のプロパティ/属性を持つオプションを選択するにはdocument.querySelector():
document.querySelector('#shipping_customer_address option[value=""]').selected = true;
document.querySelector('#shipping_customer_address option[value=""]').selected = true;
<select name="shipping_address_id" id="shipping_customer_address" class="customer_address" title="" onchange="shipping.newAddress(!this.value)">
  <option value="48" selected="selected">p p, yui, cfg, 90602-1234, U.S. Minor Outlying Islands</option>
  <option value="52" selected="selected">e B, ewri, csdfwefg, 90602-1234, U.S. Minor Outlying Islands</option>
  <option value="">New Address</option>
</select>
 
 
外部JS Fiddle デモ。
参考文献: