Based on user experience I suggest banana pro with open media vault
If OP knows ssh and comfortable with it then RPi is the best otherwise banana pro with open media vault because RPi doesn't support it
Like many others, even I would suggest a banana pi/pro. I have housed the pi and a 320gb sata-2 2.5 inch hard disk in a smps case. It looks raw but it protects my hardware well and the performance is really good. Maybe I might add a power supply in the future to the box that would enable me to run both the pi and a fan to cool it (not that it requires a fan, it's working good without any overheating)