Hi Steven,
A few general points:
* Cesium runs in a web browser without a plugin, including on many Android devices
* Cesium has a full API. Google Earth has a very limited COM API. Most apps generate KML files as a workaround
* Cesium has first-class support for time-dynamic visualization, e.g., interpolation, fixed-ICRF transform, careful treatment of details like leap seconds, ...
* Cesium is a new, peer-reviewed code-base with well over 90% code coverage from unit tests
* Cesium is open-source
* Both have been used to
track Santa. Only Cesium did it without a plugin
If you can tell us more about what you are working on, we can give you more focused points. Will you be able to share your comparison?
Patrick