I've set up websites for clients on Joomla, Drupla and wordpress. Of those systems, wordpress has had the "easiest learning curve" for my clients. Moreover, wordpress' automatic one-click script/CMS updates really set it apart from the others.
In my opinion:
* Joomla is *too* feature-rich on it's most basic install - I think it has overwhelmed my non-tech savvy clients;
* Drupal is too bare bones (without installing a ton of plug-ins; and it's script updates are a pain in the you-know-what) - causes complete lack of direction for the tech-challenged; and
* wordpress has found a happy-medium between the two.
Just my two cents.