In my experience, WordPress is the most requested platform.
Clients are already told by their friends, relatives or acquaintances that it is better to use WordPress. They would believe them and ask the web design agencies to build website on that platform itself.
Most of the forum like this also recommend WordPress. Therefore, common people would think that WordPress is the best.
In my opinion, WordPress is not always the best option. For example, I prefer Magento for building e-commerce websites. Some clients will be fine with that but some other would want to use WordPress only.