Display selected radio's value
I'm not sure I totally get what you're trying to do, but if you want to cut down a bit of the code duplication in here a good start would be to use a Twig macro.

So you'd set up your macro like this:

{% macro input(cssClass) %}
    &lt;a class=”{{ cssClass }}” href="#"&gt;Viewer&lt;/a&gt;
    &lt;a class=”{{ cssClass }}” href="#"&gt;Photo&lt;/a&gt;
    &lt;a class=”{{ cssClass }}” href="#"&gt;Video&lt;/a&gt;
{% endmacro %}

{% from _self import input %}


Then you'd call it like this:

{{ input('dual') }}


If you don't need the value of the radio buttons for anything else, you could always give them the value of your CSS class; that way you don't need to convert them from one thing to another. If you did it this way then you could just call your macro like this:

{% set cssClass = entry.viewerOption %}
{{ input(cssClass) }}


Make sure you've set a default option for your radio button when you've added it in the Control Panel.