I prefer Plex for its stupid simple "press here to share your library with your family remotely." And before the Jellyfin folks have an aneurysm, yes I know I can "jUsT uSe a ReVeRsE pRoXy" but I'm a busy guy and frankly lazy. So if Jellyfin wants wide adoption, it needs to make library sharing stupid simple.
The way Plex achieves the sharing is very convoluted and intrusive. You basically go through their servers and show them everything you have and everything you and everybody you share with are watching.
Most people who pick Jellyfin do it to retain control not give it away.
I like plex better but damn is it bloated, had to take a almost an hour digging through settings to turn all those plex features off. Now it feels more back to basics.