Most people have heard of Wordpress as a well know CMS system. It's certainly very popular and benefits from a large amount of add-ons and themes but I firmly believe Concrete5 is a better solution.
Wordpress evolved from a simple blogging platform and even now a default installation begins life as a blogging website and has to be pulled kicking and screaming into a more standard configuration for typical business website building. Concrete5 on the other hand was designed from the ground-up as a powerful, easy to use, website publishing platform, capable of building any kind of website you might require. I'm not saying you can't achieve great results with Wordpress, its just the ease of the journey* and how simple the site is to maintain on an ongoing basis for the client.
*Concrete5 won the Best CMS for Designer in the 2015 Peoples Choice CMS Awards at CMScritic.com
In terms of add-ons to extend fictionality, it’s defiantly a case of quality over quantity. The Concrete5 marketplace add-ons are all tested and approved by the Concrete5 core team - even those offered by 3rd party authors. As such Concrete5 suffer much less from incompatibility and conflict issues - resulting in a more stable platform.
But beyond all of that, Concrete5 offers a unique ‘in-context’ editing methodology which is intuitive and simple to use - no complicated ‘back-end’ list of options and menus to plough through to get to you content. Just login, browse to the page you want to update and edit it right there on-page and see how it looks straight away.
Pages are constructed from ‘blocks’ (hence the name Concrete) which can be dragged and dropped onto the page to layout the text and photo areas. All my client love how east it is to use and are often very comfortable with the system after minimal training.
Ultimately, if your chosen CMS is difficult use and every update turns into a epic of frustration and calls to your developer for help - you won’t update the site so often. One of the major factors involved in good page ranking is how often the site is updated - so its in your interest to keep the content fresh and new.
And after all, isn’t that the point of a CMS system!