I run both on my unraid NAS. I use plex for streaming to my phone over cell data. I use jellyfin for streaming to my laptops and TV.
Plex tends to break every once and a while though. Not often, but it happens enough that I'm replacing it with just having my music on a DAP that is synced with Syncthing.
I also use the comic viewer function of jellyfin.
Slammed down big style.