That it is extendable, apis are exposed to developers to use

You can tailor the editor experience to the smallest detail, Umbraco doesn't impose any practises on you, so the end product will fit the client needs, instead of you trying to fit the clients needs to the end product. In addition to that, you can extend Umbraco in any way possible, making it a great choise for both small and larger projects.

Flexiblity Community User friendliness