There is no "best CMS"! It really depends on the requirements. Some examples:
Blog -> Wordpress, ...
Shop -> Magento, xtCommerce, ...
Big Website -> Joomla, ...
However, the main advantage of a CMS is that you don't need any skills in html, css, php, mysql to style your content or store it in a database. But, for simple websites its a bit overkill to use a CMS like Joomla since you'll need to learn how it works. Imho, it's not a out of the box solution.
If you have a website with static content (like the content stays the same for several weeks) then you don't really need a CMS. So, make sure what you really want to do and then think about the best possible solution.