I use Plone to develop professional responsive websites for small and medium companies. Plone has a perfect separation of logic and templates using Diazo and a very powerful toolkit under the hood to develop any possible web application.
For my clients it is the best I can offer as a CMS, being the most user-friendly I have encountered in the last decade. Where in my price-range mainly Joomla and Wordpress websites are developed, I have a really strong competing product, offering a much less vulnerable environment. Further more it is possible to completely version-control the whole development, and scripting the whole deployment environment using Buildout.