Set default value to option select menu

You can just use v-model for selecting a default value on a select box:

Markup:

<div id="app">
  <select v-model="selected">
     <option value="foo">foo</option>
     <option value="bar">Bar</option>
     <option value="baz">Baz</option>
  </select>
</div>

View Model:

new Vue({
  el: "#app",
  data: {
    selected: 'bar'
  }
});

Here's the JSFiddle: https://jsfiddle.net/Lxfxyqmf/

html:

<div id="myComponent">
    <select v-model="selectedValue">
        <option v-for="listValue in valuesList" :value="listValue">
            {{listValue}}
        </option>
    </select>
    <span>Chosen item: {{ selectedValue }}</span>
</div>

js:

var app = new Vue({
    el: '#myComponent',
    data: {
        selectedValue: 'Two',
        valuesList: ['One', 'Two', 'Three']
    },