The reason we use WordPress today is because of its vast extensibility, extreme flexibility, and widespread support throughout the open-source community. Essentially, there is no reason to use anything else because WordPress can pretty much do it all.
Every part of the page is customizable, and everything can be managed by the client, (you) very easily. But what is even better, are the plugins. WordPress Plugins make everything incredibly easy.
As with any project, specific functionality may be required that does not come as standard with WordPress. The good news is most WordPress Premium themes can be purchased for less than $99, and a vast array of WordPress repository plugins are free. But occasionally we may recommend a premium plugin as a solution.