One contrasting feature is parametrized services: several similar processes (like agetty) can be controlled by one service directory; I find it neat.
Another difference is the ability to initiate reboot or shutdown as an action of the same binary (nitroctl).
Also, it's a single binary; runit has several.
Is that a selling point? Could you explain why?
I've heard plenty of reasons why people find systemd distasteful as an init, but I've not heard much criticism of a declarative design.