In the online marketing world, Wordpress is pretty much the standard, because it's relatively easy to configure and is incredibly powerful.
"Blogging" or regularly updating your site with fresh content is incredibly important for SEO, and from a pragmatic perspective it provides you with credibility and also, if you're publishing the right things, will encourage people to point to your site or even share your content. Which is helpful.
I've used Drupal, Joomla and Wordpress, and from a user perspective, Wordpress is the easiest to actually use as a CMS. It's also really easy to optimize for SEO.
SEO optimization in this case really means just making sure your pages and posts have good titles and descriptions - it adds to the credibility of your site, and also makes Google like you a little better.