categories - How to create a button to filter posts (list) by meta value

I have a category.php page that lists posts from each category. Above that list, I have three buttons. One that filters by title (asc), other by "most recent" and the third by "most viewed". I can get the first two to work well, but the third does not. Can anybody help?

Code:

<div id="bot-form">
                       <input type="button" value="Alphabetical order" class="bot-filtro" onclick="window.location.href='?orderby=title&order=asc'" />

                       <input type="button" value="Most recent" class="bot-filtro" onclick="window.location.href='?orderby=date'" />

                       <input type="button" value="Most popular" class="bot-filtro" onclick="window.location.href='?sortby=views'" />
                  </div><!-- fim #bot-form -->