If you look at the specs of the current NAS, plus the upcoming specs of the Synology 416, the QNAP's blow them out of the water. The current best price/performance NAS is easily the QNAP TS-453 with quad core celeron and HDMI.
The Synology 415 and upcoming 416 are in comparison much weaker... the new 416Play has some 3rd party dual-core CPU from AnnaPurna (never heard of it) and only 1GB of RAM... the QNAP has 2GB RAM and is very easily upgradeable to 8GB for cheap... not to mention quad LAN ports. Synology has nothing in the price category that can compare to that.
While I accept that Synology's software may be more refined, QNAP's OS is also incredibly mature and constantly improved (full disk encryption for the win), and in the end I think hardware really plays a bigger role in NAS longevity when you have software that is already of a good standard. If Synology don't get their act together in their highly unimpressive hardware stakes they are going to find themselves trailing badly for the next couple of generations.
I'll be picking up a QNAP TS-453 Pro and 8GB of RAM very soon and I am sure it will stream everything I throw at it (who cares about 4k transcoding, really) and last me a good while.