Umbraco is by far the best open source .NET Content Management System on the market. Being around for over a decade and built for with both content editors and developers in mind, it's a win-win application which is a joy to work on (both for us and for content editors on the client side).
The 2 biggest benefits of Umbraco are:
Aside from being a great CMS, Umbraco is incredibly scalable and can easily be extended to integrate in with third party cloud applications with minimal effort.
Lastly, and probably my favourite is to deliver the content you create through an API is one of the easiest things Umbraco can do. Ever wanted to allow someone to display your content on their site, a mobile application, build a software as a service application, create a consumption based business model and more? Well Umbraco can do this easily!