Imo they're both really good, and I like running both in parallel because some of my friends still prefer the Plex apps and UX (for example in both you can click on an actor to see other things they are in, but in jellyfin it's limited to what you have downloaded. Plex's optional discover feature means it knows about everything you don't have too, so you can click on an actor and see stuff that's not downloaded, watchlist something, then let overseerr send it to the *arr apps)

The rest of my setup would be identical if I was just running Plex or jellyfin and when they idle they don't use any CPU, so I don't see much of a reason not to run both and let people decide which one they like. They also both use quicksync, though I had to change some settings manually in jellyfin to get it to work. I just point them both to the same media folder and it just works.