clientexec is not a CMS but a billing manager. CMS stands for “Content Management System” something like WordPress, Joomla, PHP-Nuke etc.
I was asking about the best CMS.
There’s no such thing as a best CMS. Each will be better for some people, for some purposes. Wordpress, while built for the purpose of a blog, can be used successfully for other types of sites, and it is, IMO, easy enough to use.
I often use Joomla, but that may simply be due to habit.
In my opinion, the best CMS operating in the market is Joomla! The next good one is Drupal. You can check out these, and see if these match your requirements.
Try Silverlight perhaps? It’s quite simple and looks good. I have never liked using Drupal or Joomla. You might love it though.
Wordpress is really meant for blogging. However it can be used as a CMS quite easily. Just be prepared to customise it heavily to make sure it doesn’t look like “Just another Wordpress site”.
What kind of a site are you desiring to build? There is no one CMS which will fit every purpose.
Besides the already recommended WordPress, Joomla, & Drupal, the following are worth considering Jaws, glFusion, e107, ocPortal, Concrete5, Exponent, and Xaraya. You can find a short description and demo of many CMS solutions at [OpenSourceCMS](http://php.opensourcecms.com/scripts/show.php?catid=1&cat=CMS / Portals).
It really does depend what you would like to do. If you’re looking to make a website go for Joomla/Drupal and if you’re going to be making a blog go for WordPress.