New Twiddle

app.helpers.is-equal.js

import Ember from 'ember';
export default Ember.Helper.helper(function equalHelper(params) {
  return params[0] === params[1];
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  choices: ['red', 'green', 'blue'],
  value: 'red'
});

templates.application.hbs

<h2>Choices</h2>
<select onchange={{action (mut value) value="target.value"}}>
  {{#each choices as |choice|}}
    <option value={{choice}} selected={{is-equal value choice}}>{{choice}}</option>
  {{/each}}
</select>

<h2>Selected Value</h2>
{{value}}

twiddle.json

{
  "version": "0.4.7",
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/1.13.6/ember.js",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/1.13.7/ember-data.js",
    "ember-template-compiler": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/1.13.6/ember-template-compiler.js"
  }
}