I have tried both WordPress & Joomla before when I was trying to learn the new CMSes several years ago. My very first impression was that WordPress was so easy to pick up straightaway without getting too much detail, however, Joomla was totally the opposite. It was really hard to understand and it took lots of steps to get one page setup.
A few years has passed and I am stick with WordPress. It works great and meets all my needs, so I have not re-tried with Joomla since then. Red Giant Design has kindly produced an infographic compare those two CMSes in detail. And again, it proved my original theory / experience.
I have also tried Drupal recently and found that it is quite easy to use and learn. And I am currently building a website for my friend using Drupal. From my personal point of view, WordPress is great for personal blog, while Drupal & Joomla are designed mainly for building business / commercial website using CMS tools.
I hope they (Red Giant Design) can produce another infographic detail the differences between the three would be awesome.
Keep up the good work!