I have a QNAP TL 569 which I generally like, although I am tempted to upgrade to a big Synology system, for none other than more storage and ease of use. I managed to figure out a lot of the QNAP's setup, but the Qsync still escapes me. They could really make it a bit more intuitive, as in if you are syncing things, it is generally between two entities, show me which entities in your browser, so I can see which it which, I mean really.
From my reading, QNAP and Synology seem to be the best rated and I haven't had any issues with teh QNAP other than non-intuitive settings.