A synology nas is nice because it is a separate box, an easy to manage. The downside is it can run you $1000 for just the nas and nothing else.
For me I already had a file server tower with 8 3.5 bays inside. I have a JBOD raid card that will support 8 drives and a software called flexraid.
This allows me to pool the drives together (and they can be completely different sizes) and once a week it will run pairity. It also means that I can have the data protection without having to spend a lot of money on raid/enterprise drives.
For movies this is just fine because once you put the movie on the drive you are likely not going to do anything with it. For large databases or system/user files this would be a horrible solution because of how frequently the data changes.
Then in the living room and guest room I have a couple of cheap PCs running openelec distribution of xbmc.
For a front end xbmc or plex are your two best setups. plex is lighter on the client and you can even get a plex channel/add-on roku and other devices, while xbmc requires a pc (or jailbroken apple tv), xbmc can run on windows or Linux. While xbmc is heavier it has a tremendous amount more customization and a much prettier front end with many aftermarket addons, all configurations are xml pages that you can customize to your desire.