Personally here is what I saw when first tested both years ago:
Joomla = News and informational publishing site with lots of articles/contents and more updates for different categories
WordPress = Blog and company site made for marketing purposes and presentations of a products
Conclusion:
Both platforms can be modified to various purposes, but
a) If you will provide lots of information many updates and easier search (and search integration) and presenting them the Joomla is the right choice
b) If you want site that represent you/your company with more graphical /show effects and you do not need large amount daily publishing then go for WordPress as it is more like a FB wall