Every Linux device needs an init program of some kind. If you are designing a system, which only has to launch a small number of daemons at startup and remains fairly static after that, then BusyBox init is sufficient for your needs. It is usually a good choice if you are using Buildroot as the build system.
If, on the other hand, you have a system that has complex dependencies between services at boot time or runtime, and you have the storage space, then systemd would be the best choice. Even without the complexity, systemd has some useful features in the way it handles watchdogs, remote logging, and so on, so you should certainly give it serious thought.
Meanwhile, System V init lives on. It is well understood, and there are init scripts already in existence for every component that is important to us. It remains the default init for the Poky distribution of the Yocto...
