ive been using kodi (xbmc was better moniker) since google killed sagetv. i recall attempting plex, but it seemed to lack some open/extensibility (its been awhile).
i have a side project i want to make as a modular plugin generating a cable layout with original air orders and networks/channels… kodi seems most optimal, but ill admit its been a long while since i looked at plex.
so why plex over kodi?
They're for different things: Kodi is supposed to be used only on one system inside your network and is full of eye candy. It's roots are as a media app and dashboard for the original Xbox. It doesn't have any streaming functionality, it expects the media to be available locally (either physically attached or over a network share attached to the local system).
Plex was originally designed as a media server and has a Client-Server model to support multiple clients both inside and outside the network. It's more about functionality than looks. It was built from the ground up for streaming.
You can use the Kodi frontend with the Plex backend with a Kodi plugin called PlexForKodi. Same goes for Jellyfin.