Raw Source
swole_hamster / Auto-select Amazon Payments 

// ==UserScript==
// @name         Auto-select Amazon Payments
// @version      0.2
// @description  Changes auto-selection from gift card to payments balance
// @author       Tjololo
// @match        https://www.mturk.com/mturk/transferearnings*
// @require     http://code.jquery.com/jquery-latest.min.js
// @grant        none
// @namespace https://greasyfork.org/users/710
// ==/UserScript==

$('input[value="AmazonPayments"]').click();