Just a personal opinion.
In the years I have been using D-Link DNS-343 (since its first launch till about slightly more than 8 months ago), I have been faithfully waiting and waiting for D-Link to really pull up its socks to really give its NAS product a real solid push in terms of its firmware stability and probably some of the basic features which other NAS makers already have in their products.
Sad to say, I have finally give up hope and abandoned D-Link. D-Link is just not what it used to, with the changes (internally) that happened in recent handful of years.
Having been on QNAP for the last 8-9 months, I have been a very very very satisfied customer and still so excited about the TS-459 I have as every quarterly or so, the firmware update not only packs fixes but new features and also updating to support latest basic infrastructure services (such as Mac OS X Lion Server Open Directory, AFP). I would say, I will never look back again and never going to recommend D-Link NAS again even to friends and acquaintances. Just simply one reason: "Importance of NAS (storage) has grown so much even in SOHO or Home infra that an unreliable NAS (high risk of data loss) is just not acceptable."
Nowadays, NAS is used to store GBs (if not TBs) of precious photos and videos which are precious memories and moments of life that are not replaceable. Who wants to invest in a RAID-capable storage device that isn't any better in fail-safe/redundancy than what a PC-onboard SATA RAID can do?!
Just a consumer perspective.