As Drupal experts, we use Drupal for sophisticated, 'professional grade' sites which need a lot flexibility and custom features. It is also ideal for sites requiring the highest level of security. Drupal has its own security team, and undergoes rigorous audits by the US government in order to be authorised for use on such sites as that of The White House.
Drupal tends to cost significantly more to build and maintain than Wordpress, because it can be time-consuming, and because Drupal specialists are in great and ever-growing demand. In addition, Drupal places a large burden on hosting services (though with proper setup and quality hosting rather than cheap generic hosting packages, Drupal can be fast, as the speed of the present site should demonstrate). In cases where the budget is available, it is the most advanced and powerful Content Management System (CMS) software available. Drupal can also be used for relatively simple sites, and some clients prefer it. The present site is made with Drupal: it is a simple site which could be made in Wordpress, but we just like Drupal!