When you choose a 3D rendering stack to work with your 3D city model, your best options are open-source: CesiumJS, VTS Geospatial or iTowns. While it is not trivial to make a direct one-to-one comparison because each stack is built on slightly different philosophy, they all strive for the best possible performance. In this talk we will discuss the strong points of each stack and show a performance comparison between them carried out on the same data. Possibilities of interoperability and hybrid architectures will be also briefly covered.