Well... The main advantages of these two are: Joomla provides many good quality templates/design stuff...while Drupal is more suitable for programmers and is better for the website's functionality.
One drawback for Drupal would be the lack of good themes. Drupal has a better SEO page titles/description/urls and so on. The documentation is larger for the Drupal CMS. The user system is better in Drupal. The shopping cart is better in Joomla. Commercial Comunities are better in Joomla.
So you see, they are almost equal, thus many discussions about which is better. If you are looking for functionality,sacrificing beauty , you should choose Drupal and start installing those modules. If you want a website that looks good but doesn't have that much functionality, you should choose Joomla. I tried Drupal, and as an example check the website in my signature. Cheers