Using 3D Models in Cityengine, Cesium and 3D scenes

I recently started working with 3D models, and the following question may be a bit too abstract? If I need to build a 3D city with buildings and other features, what software should I use as a database, editing and displaying the result as a web map. I may be comparing apples to oranges, but maybe I can get a general overview of the available softwares and their possibilities and limitations.

I have previously only heard of Esri solutions, such as CityEngine and 3D Scenes. I have an ArcGIS Pro with data interoperability extension, so I can use FME if needed. What is the difference between CityEngine and 3D scenes, how are the files exported to a web service? Do I have to use the ArcGIS Online for representation, or can I use ArcGIS API for JavaScript so I can display them in other apps? What can I specifically do with ArcGIS API for JavaScript as it pertains to 3D modelling and web maps?

There is also an open source solution called Cesium. I have never used it, but it seems to have similar functions. How is different from Esri?