So Emby is now closed source? Wow. I didn't get that message. Not that I really care about that for a media server, but it's still strange that I didn't realize that.
I think that the main problem with Plex (some of those are the same as Emby) are:
* They are trying to add too many features (Plex Arcade? really?) while other features are not stable - chromecast queuing was working then not working then working again with every other release. In the end it stopped working for a while, and I quit using Plex. I just need something to have my collection organized, with a bit of metadata handling and a "watched/not watched" flag. Plex (and Emby) are trying to do an incredible amount of work on top of that.
* The price for the "deluxe" version is too steep for a self hosted solution. Netflix Standard is EUR 144/year, Plex is 40 EUR/year (about the same as Emby, btw). And I need to provide hardware, electricity, and content - it's just not competitive. I'd be happy to pay something between 10 and 20 EUR per year for a properly working software of that kind.
I'm a reasonably happy Jellyfin user as well. On the one hand I'm grouchy to not have native apps for phones, PS4, etc; on the other, it seems to work pretty reasonably just through a browser.
I dropped Plex because its quality was getting lower and lower, especially chromecast-wise.