I have both. I really dislike the navigation in Jellyfin. It seems impossible to elegantly move between various collections compared to Plex, which just seems to fit my brain better.
That said, my daily driver is actually Infuse, which points at the Jellyfin server because:
Infuse has the most reliable playback and never needs transcoding (Synology server, AppleTV client)
Infuse will purge its cache and have to rebuild/refetch all the metadata for my library. Pointing it at a Jellyfin server allows all that info to persist including custom posters etc.