Depends on the usage and also service. I’m using subfolders for all my Tasmota switches. Like https://switch.domain.org/garage this makes it easier to maintain because I don’t need to mess around with a new subdomain for ever new device. On the other side, I like unique services on a subfomain: video or audio. I can switch the application behind, but the entry point remains.
I’d recommend: https://docs.linuxserver.io/images/docker-ubooquity Easy maintainable and very comfortable to read the ebooks with any browser or download. Also supports multiple users.