Actually if you said "Hey you use free blogging platform and subdomain, what makes you write this article?" Ah come on I also have another blog that installed with paid hosting service, but this blog is my second blog at blogspot. Hmm OK back to topic how to choose the best CMS for new website? CMS is Content Management System, and CMS only for website that offering information to their readers, CMS absolutely not recommended for corporation profile website or another simple website, because CMS only wasting your database and space. When I heard CMS I spontaneity remembering Wordpress by Automattic, then Joomla, and third Drupal. Because they are super famous CMS, nobody doubt it. So it's easy to choose the best CMS for you, if you want to build an information website just use one of them, but if you want to build simple website just use PHPNuke, that PHP script has high flexibility.
You should considering CMS by these points;
1. Ease of use
2. Ease Support
4. Compatibility with current web standards
5. Turn over period