Personal preference, really. For me, jellyfin is much simpler to use, very easy to self-host in docker. And the clients are great too. I use desktop, android and roku regularly.

Better is subjective.

Simpler in a more streamlined sense, yes. Plex is more hands-off, and is doing a lot behind the scenes to automatically configure itself to your hardware for the best transcoding experience and such.

Jellyfin needs a little more work but can get there, it just needs to be shown the hardware and be configured correctly, but I find Jellyfin to be simpler and less cluttered overall when properly finished, with less strings attached to a parent company.

Client apps are more limited but otherwise floss purist swear by it