** i've worked with joomla for years:
- joomla sites are unusually slow to load, probably due to joomla's over convoluted code
- for a newbie it's relatively complicated to set up and maintain
- joomla is relatively frequently updated, but these updates often revamp the software in a major way, causing users to spend tons of time adapting their sites
- joomla extensions (addons) are 99% absolute crap, badly coded and super over complicated to use, plus give a very poor user experience (look and feel bad to site visitors). the few addons that are actually good (e.g. jreviews) are relatively expensive.
in short - i wouldn't recommend joomla, definitely not to a newbie and not even to an experienced webmaster due to joomla sites being so slow and time spent on maintaining them.
** wordpress: also worked with it for years (although less than with joomla), it's ok.
** drupal: comes highly recommended by many, but haven't worked with it myself.