I've got a dedicated Mac mini server, two minis used as entertainment centers, and four additional Macs. Using Plex, and the server has many other services not pertinent to this discussion.
Our son gave my wife an Apple TV last Christmas, and I retired a Windows PC that was also being used as an entertainment center. It turned out to be a real PITA.
- I now had to run iTunes on the server as well as Plex and iTunes is a real resource hog.
- Any videos I wanted to view on the ATV required importing into iTunes.
- I didn't want to use iTunes on the Macs because the UI isn't as nice as Plex and there is also a 5 system home sharing limit which I would exceed.
- My wife found the ATV remote and the UI confusing. But this was before I found out that I could use Parental Controls to get rid of all the video channel selections we would never use. This was never an issue with Plex (or ROKU).
- I was able to get the ATV to work with Plex as a source, by commandeering the Movie Trailers channel, but changes made in an ATV update broke it and getting it to work again would have been very time consuming.
- I finally dumped the ATV for an original ROKU that was sitting in a closet. This works great with PLEX and all the other services I care about (Amazon and Netflix, primarily). Still running PLEX client everywhere else.