Umbraco is a focussed CMS. It is fully-featured, open source and flexible. Over the last decade, we have developed multiple Umbraco sites a year and continue to support them post-live.
We select Umbraco over Kentico when just content management is required out-of-the-box. Kentico offers a wider scope of functionality than Umbraco. Umbraco is more focused, has no licence fee and is more of a framework.
That framework approach makes integration and extension easier.