Should I use WordPress or Joomla for my new site?

The basic purpose of any CMS is to allow a non-technical administrator to easily enter a site's content into a database, and then display that content in the correct format to the user. This administrator should not need to have any coding skills.

For a website, this front-end code is generated by outputting HTML5 markup, which can be interpreted by the user's browser to display the page. HTML5 will be the output format regardless of which CMS you use (assuming you want the content to render in a browser).

For a user (or a search engine), as long as your code is valid & semantic and your site runs fast, which CMS you use makes no real difference. Both Joomla and WordPress allow you to optimise your site's output code however you want, and both can generate high quality front-ends that work well for usability and SEO.

The main consideration you need to make when choosing a CMS regards ease of building and maintaining the site. A good rule of thumb is to ask how many of your requirements (including future requirements) are achieved out-of-the-box. For example, if you're building a shop, then you are better looking for a shop CMS than trying to turn a blog into a shop.

WordPress can make an excellent blog or news site, as it was originally designed to just be a blog. However, it doesn't have a strong framework for professional development, so extensions often contain a lot of spaghetti code when you look under the hood. For example, we've seen shop extensions that place order details in tables of the database relating to blog posts. Whilst a user would not notice anything amiss here, this means the site would be very difficult to disentangle if you needed to export the data for use elsewhere, or fully remove the extension.

Joomla provides a far better framework for developers building bespoke extensions, and so development of extensions will generally proceed more smoothly, and be less of a headache to maintain in future. It also has a larger library of out-of-the-box functionality for non-blog requirements.

This is not to say that bad development cannot happen with Joomla (or people cannot enforce their own good development practises within WordPress), just that if a site is more complex than a blog, we tend to favour the framework-driven approach of Joomla.