I used to use Joomla exclusively. I think I've read the phrase "Google loves Wordpress" about 12,000 times on this site. Google doesn't care about your CMS. Joomla does just as well, and without a plugin. However, I eventually saw a WP template that I really needed, installed it, started to play and I was hooked.
Joomla v Wordpress (sorry, never used Drupal)
SEO: Equal results from my experience. You can do all the necessary on-page SEO with both pretty easily.
Design: for the plugins and themes, Wordpress by far. I also find it easier to manipulate themes with WP.
Ease of Use: Wordpress. I prefer it's console, widget and plugin management, and editability. Joomla's module setup can be annoying.