WordPress and Joomla are both written using PHP and they both perform best when running in a Linux environment. WordPress is more popular than Joomla and there's a perception that Joomla is harder to learn. This may be true but the main difference is less about complexity and more about the way each system is structured. In simple terms, WordPress is more flexible and preferred by designers who find Joomla's structures restrictive. Joomla on the other hand is favoured by more technically minded people who prefer its more logical structures.