Hi First thx for a intressing website and Youtube channel. I have today since a couple of years a WD pr2100 wich has served me well. I use it mostly for Plex and some minor backups. I also have some friends who uses my Plex server. I think of upgrading to get more bays and a more powerful NAS. I have consider synology 918+ or 920+ or maybe a terramaster. But recently I also have been looking at the qnap 672N-i3. Regarding on more Plex users is the qnap a better choice? Mainly the material is 1080 p. Is it more futureproof regarding some 4K with the qnqp ? Is there another better NAS option ? I have ofcourse Plexpass with transcoding today on my wd pr2100. I dont mind spending some money on a new NAS.
Both the Synology and the QNap devices you mentioned are great choices. In my opinion, it really comes down to User Interface, when choosing between the two. Go to the companies site and demo the interfaces. See which one you like the best and then pick your hardware. As for the Terramaster, I have no experience with them, so I cannot comment.