
I have been using both them for designing websites for over a decade but I incline to use Joomla more than Wordpress, and there are a few reasons for that:
- as a web developer I can develop extensions (components, modules, plugins) for Joomla more easily that Wordpress modules. With them the developer can extend the website in any direction you want.
- each CMS has some advantages and some disadvantages. Misconfigured they both can be slow and can consume a lot of resources, and debugging them can be awful in some situations. In some cases you can only rebuild the website instead of repair it, but that's another story.
- you can design a website in just a few days if you have the experience. There are enough templates and template builder to pick one, for free or for money. You should only read its documentation to check the compatibility with your Joomla version and its required resources.
- choosing a good template will get you a fully responsive website, and you can check it during the development.
- a disadvantage is the Joomla updates (from a version to another and from a major version to another): the update can sometime ruin your website and you should make a backup copy before starting the update.
- this website currently have about 17,200 articles added in the last 14 years, and it's designed in Joomla (migrated on Joomla, to be entirely clear). And it's reacting fast enough because it's optimized for that (as part of SEO).
One good issue: there are enough CMS on the internet to use the best one for you and / or your project. For some procjects Joomla is perfect, for other projects you can use Wordpress or Cakephp. It's your call, and if you are not sure what's the best option contact someone with experience.