I create all my sites using WordPress and have been for the last 3 years. The reason I continue to 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. For example, if need something to help you create a form that your customers can fill out, there is a free plugin for that. Think of it like an app store, for your website.
WordPress can do it all, take a look at these sites done with WordPress:
Check out My Work for some examples of customized WordPress sites that I’ve done.