Radio buttons on Rails

Similar to this question: Checkboxes on Rails

What's the correct way of making radio buttons that are related to a certain question in Ruby on Rails? At the moment I have:

<div class="form_row">
    <label for="theme">Theme:</label>
    <br><%= radio_button_tag 'theme', 'plain', true %> Plain
    <br><%= radio_button_tag 'theme', 'desert' %> Desert
    <br><%= radio_button_tag 'theme', 'green' %> Green
    <br><%= radio_button_tag 'theme', 'corporate' %> Corporate
    <br><%= radio_button_tag 'theme', 'funky' %> Funky
</div>

I also want to be able to automatically check the previously selected items (if this form was re-loaded). How would I load the params into the default value of these?

As in this previous post, with a slight twist:

<div class="form_row">
    <label for="theme">Theme:</label>
    <% [ 'plain', 'desert', 'green', 'corporate', 'funky' ].each do |theme| %>
      <br><%= radio_button_tag 'theme', theme, @theme == theme %>
      <%= theme.humanize %>
    <% end %>
</div>

Where

@theme = params[:theme]

Same as V's, but has associated labels with each radio button. Clicking the label checks the radio button.

<div class="form_row">
  <p>Theme:</p>
  <% [ 'plain', 'desert', 'green', 'corporate', 'funky' ].each do |theme| %>
    <br><%= radio_button_tag 'theme', theme, @theme == theme %>
    <%= label_tag "theme_#{theme}", theme.humanize %>
  <% end %>
</div>

Using Haml, getting rid of needless br tags, and nesting inputs within label so that they may be selected without matching labels to ids. Also using form_for. I would consider this to be following best practices.

= form_for current_user do |form|
  .form_row
    %label Theme:
    - [ 'plain', 'desert', 'green', 'corporate', 'funky' ].each do |theme|
      %label
        = form.radio_button(:theme, theme)
        = theme.humanize