My move from Plex to Emby is complete. It went smoothly and I can say that in many ways, for me, Emby is easier to use and more complete where it matters most to me.
My setup is simple:
I do NOT share with anyone.
I did not use music or other audio through Plex and that is not changing with Emby.
I do not use any type of DVR to record from a tuner.
My server(s) and my media are all on the same network.
Now on to observations and other info:
My Library is all named (both Movies and TV) according to Plex standards and Emby imported everything first try except for two movies that always fail on a new Plex install as well. Emby also exposed two misspellings in my file system that had caused Plex to actually mismatch two other movies. Plex had those wrong but I never watched them so I did not know until Emby did not match at all. I prefer that if the system is not sure that it does not match at all so here Emby matches better than Plex.
The libraries (that is the movies or TV shows in them) do not become much available for playback in Emby until the first scan of the library is finished, or nearly so. I do not really consider that a weakness or a strength, it is just a difference.
The Shield TV and Fire TV apps are VASTLY superior in Emby. I used those and the Roku app during testing and I have to say that for Emby, although the Roku app is quite good, the Shield and Fire are both better. In fact Emby on an old Fire stick is quite usable.
The collection implementation in Emby is WAY better than what passes for it in Plex. There is an "automatic" collection function that I did not test but it only takes a few minutes to add a large group of movies to a collection. Emby does have a weakness in their collections in that the only sorts available are "date released" and "name" and you cannot change the sort of a collection inside an app. It can only be done from the server.
Speaking of sorting there are few sorting or filter options in the apps in Emby and you cannot reverse a sort except in the web app.
In Emby you cannot, at least yet, exclude a library from the dashboard.
Emby require NO web connection to stream locally and, from what I understand, even to remote users. The streaming goes direct and is never passed through any Emby servers or processing.
Users seem easier to create and maintain and can be set with parental controls and library restrictions but I have only tested this slightly as my granddaughters will not be visiting until December.
Transcoding is less strenuous for the server. Also it seems, for me, to make better choices as to exactly how it transcodes and to what.
There are other little differences that are too numerous to mention but no real irritants that I have run into.
I am leaving my Plex server installed on my Shield as in does not impact anything and it is good to have a backup but I do not plan on using Plex unless something really unexpected happens.
I will continue trying to help people here but I have now calmed down somewhat so I "think" I will be less negative but who knows. Mood swings, along with some other things, come with age. The Emby forums are a lot less active and the entertainment factor is lower so these forums are more attractive for that.
I am sure I left out some (maybe a lot of) things that would be of interest to some people and anyone should feel free to use this thread to ask questions about the differences between Emby and Plex but let's keep the "how do you" questions about Emby in the Emby forums and limit ourselves to just differences and/or possibilities in this thread.