As a Bevy contributor, I can say that rg3d is much more mature and feature-complete than we are right now. They're substantially ahead on animations, UI, sound and rendering.
That said, the engine isn't ECS-based (they use a scene graph instead), the community is much smaller, and the engine as a whole seem to be much more narrowly focused on a specific type of 3D game, exemplified by the shooter example.
That said, the engine isn't ECS-based (they use a scene graph instead), the community is much smaller, and the engine as a whole seem to be much more narrowly focused on a specific type of 3D game, exemplified by the shooter example.