2012R2 is very stable, we have a system that had it preloaded when it was first released, it still works to this day (why wouldn't it?), the hardware might be f**ked, MemTestX86 it, it's probably RAM,
anyways, it's annoying to figure out what OS you are going to use as a NAS OS
i usually weigh it with these criteria:
1. what OS's is most dominate on the network?
2. what OS has the features you need? and how well do they work with your current setup?
3. how easy are they to manage, is their interface simple or advanced? (GUI or command line (cmd or terminal))
4. how much can you automate the server, are these tools built into the system, third party downloads or custom (if you know some command line commands)
5. how well does it preform with the tasks you intend to do?
this is some of them
i have at least 2-300 criteria i go with and if all of the boxes are ticked, it's the choice for you!
sorry if this is too much for you to do, i don't use this list often and only use it when deciding a new OS for a new or existing server...