I agree with the other answers, radio buttons are the best choice for an input with 3 choices. According to GNOME developer, they are preferable for your problem because:
Radio buttons are used in groups to select from a mutually exclusive set of options.
https://developer.gnome.org/hig/stable/radio-buttons.html.en
Radio buttons or a list will often be preferable to a drop-down list, as they present all the available options at once without any further interaction.
https://developer.gnome.org/hig/stable/drop-down-lists.html.en
Unfortunately, the default style of radio buttons is boring, but the .btn-group
class from Bootstrap can help you to improve the style of your radio buttons:
(or) 
JSFiddle demos :
The downside is that it requires jQuery, Bootstrap CSS and JS (see the External Resources tab on these JSFiddle links for the CDN URLs).
Here is the HTML code:
<div class="btn-group" data-toggle="buttons">
<label data-value="yes" class="control-label btn btn-default" for="button_1">
<input id="button_1" name="opinion" required="required" value="yes" checked="checked" type="radio"/>
YES
</label>
<label data-value="no" class="control-label btn btn-default" for="button_0">
<input id="button_0" name="opinion" required="required" value="no" type="radio"/>
NO
</label>
<label data-value="no_idea" class="control-label btn btn-default" for="button_void">
<input id="button_0" name="opinion" required="required" value="no_idea" type="radio" />
No Idea
</label>
</div>