The 3D Tiles tiles specification and implementation will eventually supersede the QuadTreePrimitive, but that probably won’t happen for a while. Both can be used for quad-tree LOD visualization.
Cesium doesn’t support dae files directly for a variety of reasons and instead uses glTF, which is the new Khronos standard for runtime model formats (particularly on the web). So you’ll need to convert your data either way.
QuadTreePrimitive is marked private and is not officially supported as part of the public API. It will eventually change or go away in the future. That being said, many users have had success using it in their application (search the forum for more info). Any approach using the QuadTreePrimitive will have involve converting your individual models to glTF and loading them whenever they tile they are in is needed. Depending on the size and complexity of your model as well as the number of models per tile, this may or may not perform well for you.
3D Tiles are in heavy development, the NYC demo (http://cesiumjs.org/NewYork/) links to sample data which you can serve locally. There is a Cities Sandcastle example that can be used to load it in the 3D-Tiles branch. Because of the nature of 3D tiles, performance will be much better than the QuadTreePrimitive approach, but you’ll need to write code to create the tiles yourself since no public pipeline is yet available.
If you want something that “just works” your best bet is to wait for 3D tiles to be ready. However, if you want something sooner, you may want to try and create your own 3D Tiles from your dae files and use the branch. This will be more future-proof than building on QuadTreePrimitive. See this blog post for more info on the tiles spec: http://cesiumjs.org/2015/08/10/Introducing-3D-Tiles/