Over the past 3-4 years I have run Plex on a Western Digital PR2100, Synology DS916+, and currently a Synology DS918+. Synology has been the best experience for me. The Western Digital is VERY limited in scope of what it can do. Yes it works fine for storing files, and running Plex, but it is a pain when it comes to firmware updates, app updates, managing it’s limited settings etc. Anything else is better.
I Switched to the Synolody DS916+ (which has the same processor as the WD), and it could do so much more! Virtual Machines, Docker, Mail hosting, VPN, DNS, the sky is the limit. I gave the 916 to my dad, and I now run the newer 918+ (which has a better processor, and two M.2 slots for SSD caching)
I recommend the Synology DS718+, DS918+, or DS1019+ (just depends on how many drive bays you want.) How much storage are you planning to need/want?
Here is a post I made on another thread (take note of my first point for a comparison between the 918+ and the 1019+, and the fourth point for 4K media):
