Wordpress is still the leader of CMS today for website, they have more good themes and plugins that you can make your website look professional. For SEO aspect, you can more plugins that support SEO for wordpress as SEO by Yoast, All in One SEO Pack, Google XML Sitemaps..etc
Although it is leader but it is not the best because it depends on customizations that you can do for your site, if you can do well both on page and off page SEO for your custom CMS then it still can be better than Wordpress.
Hi well i will agree that WordPress is the best CMS I find Yoast and all in one seo increasingly bloated so i switched to and now recommended
The SEO Framework
it does everything the above mentioned plugins in a much lighter package and no dashboard ads https://en-ca.wordpress.org/plugins/autodescription/
I'm not an expert on SEO (probably something I should look into) but I would think WordPress has the best SEO. As stated above, WordPress has many tools which can also improve SEO. But again I could be totally wrong! If I am, please correct me!