Bit late... but definitely avoid Seagate Greens and WD Blues. The modern day Greens in particular do NOT have the tolerances to deal with the drive vibration of a NAS anymore. As G8torbyte said the HGST drives are good and 7200RPM however they are LOUD, so if you are sleeping or listen to music in the same room as the NAS you will not be happy. HGST drives are the loudest possible of the lot, in rotation noise but even more when seeking.
Seagate IronWolf drives can be found for $25 a TB or a bit less on sale every ~3-4 months. I'd strongly recommend those if the NAS data or reliability is important. But shucking enclosures for some WD Reds should work fine too.
I like having a NAS given I have a few PCs and tablets on my home network that interact with the data, though 1gbit ethernet definitely limits performance. I do find near 100MB/s read/write is sufficient for what I need, but involves some waiting for large transfers.
I've started to eye a new box over my Qnap TS-431, something that will support 10gbit, along with the required upgraded switch and 10gbit card for my main PC at least. Probably the 8-bay TS-832X-8G which seems like a good natural progression.
Right now I have two 4TB WD RED and two older 3TB something or others in two RAID1 volumes (so ~7TB total usable capacity). The two 3TB drives were carry overs from a budget 2-bay build many years ago. Even the 4TB drives are probably 4 years old and I've never lost a drive.
Given pricing, I'm considering shucked externals for my next build. They're almost half price, often ~$180-200 on sale for 8-10TB drives instead of around $280-310 for "NAS-grade" drives. I'd really like to start with a 4 or 5 drive RAID6 in a TS-832X-8G, which is looking like $2k in total. A steep price tag for my upgrade project. I figure Even if I end up with some failures there are reports WD will honor a shucked drive return, and unless I'm pretty unlucky the money saved will easily pay for a few replacements over the years. Also it seems sometimes WD puts RED drives in their externals, but you may get the white-label (aka blue?) drives. From my reading I'm not sure it is super important.
Can't tell you how much I hate QNAP right now, so I'm definitely biased. My TS-431 had a defective SATA controller, but the device never let on in the error logs about it and hid the error from me.I didn't discover this until a HDD "died" and I bought a new set of drives.
Turns out they would work but not fully initialize in the unit. QNAP support had me install some diagnostic software that pulled hidden logfiles from the NAS, and only then did I gain access to logs showing the hardware controller was not able to fully communicate with drives. Of course this was <2 months after the 2 year warranty. The same SATA port had started to occasionally drop from the array when the unit was still under warranty, but without pulling the hidden logs users would never know.
Drive IO errors are just one of the things Seagate's IronWolfs will detect and warn users about. They also have vibration sensors, shock sensing, temp monitoring and good tolerances. Today QNAP now supports IronWolf Health Management but they didn't last year. The drive would have been able to inform me that the NAS itself was defective and save me money on those shucked disks I never got to use. Or from having to buy a new NAS.