I went for the TS-451, its kind of in the middle, not too budget, not too hardcore.
http://www.amazon.co.uk/QNAP-Performance-Network-Attached-Storage/dp/B00KXP9RJC/ref=sr_1_1?ie=UTF8&qid=1456466963&sr=8-1&keywords=ts-451
I wasn't really too fussed about throughput / bandwidth etc...