It really depends on the business, their requirements and what they are looking to achieve from a website. Both systems will work fine up to a certain point. If you want to integrate with other business applications and systems then Drupal is by far the greater CMS, using WordPress you will possibly hit some issues. However, if you need a website online in quick time, and have a limited budget, then WordPress is fine. Drupal is a little harder to install and configure,

Saying that, we love WordPress, our site is built in WordPress so we love the system.

Security wise, Drupal wins hands down every time. The Drupal Community work very hard to keep their systems secure, safe and adding new features. WordPress, and how their community/marketplace works (for themes and plugins) is not as good as there are many plugins which are not kept up to date, and can just break the site if used. Using them they can also put your WordPress site at risk too.

Good luck to everyone exploring systems!