As part of my professional development I want to learn about building sites using CMS tools.

I know a bit of WordPress but it seems more like a blogging "pure play".

I`d like to expand what I know by learning EITHER Drupal or Joomla.
But I dont know enough but either to make an informed choice about which to choose.

I`d like to know what the strengths and weaknesses are of each program.

Some people say that in simplistic terms -
Joomla is for Designers, Drupal for Developers

Joomla:
pro - easy to install
pro - alot of features you can install
con - break something and you will cry trying to fix it
con - custom modification to the code are hard and painful

Drupal:
pro - Much cleaner code. Easier to modify.
pro - Less bloated. Less features.
con - Does not have the user base of joomla (not as popular)
con - Not as easy to use as joomla

Pod.

Joomla: more user-friendly
Drupal: more developer-friendly

I've never used joomla, but drupal has tons of user submitted modules that are really easy to add to your site.