Tong Family

Well, reading BackBlaze statistics (although the statistics are controversial), it is pretty clear that the Seagate 3TB have huge failure rates (25% plus annually). We have five Seagate 3TB from 2012 and now four of them have failed. It’s another reminder that it would be good to have RAID and ideally get to ZFS with automatic scrubbing of data.
And Vlad has recommended that using RAID1 is better if you don’t care as much about cost because it is trivial to rebuild it.
So whats a good SATA drive to get if you’ve got a consumer chassis. For enterprise, you probably want something like gnarling SAS (we built one for work). What’s in between would be SATA drives with 10^15 reliability.
They do cost more. Anandtech shows theres a dividing line between consumer NAS drives and professional, so choices for 6TB are:

• HGST Deskstar NAS. 10^14, 3-year warranty, 7200rpm, 1M hour MTBF. $300 HDN726060ALE610
  
• WD Red. 10^14, 1Mh MTBF, 135TB/year, $266, WD60EFRX

For the higher reliability ones at 10^15, so by pure specs, the Hitachi Ultrastar He6 seems like a good deal

• Hitachi Ultrastar He6. 7200rpm, 2M MTBF, 550TB/year, 5 year warranty, $430, HUS726060ALA640
• Seagate Enterprise Capacity v4. 7200 rpm, 1.4M MTBF, 550TB/year, 5 year warranty, $430, ST6000NM0024
• Seagate Enterprise NAS. 7200rpm, 1.2M MTBF, 180TB/year, 5 year warranty, $440, ST6000VN001

Right now however on a cost basis, the 4TB drives are at sweet spot that Anandtech reviews with the more consumer grade 10^14 drives:

• HGST Deskstar NAS. 7200 rpm, 1M MTBF, 3 years, no TB/year, 600K L/uL, HDN724040ALE640
• Seagate NAS. 5900 rpm, 1M MTBF, 180TB/year, 3 year, ST4000VN000

And here are the 10^15 ones that are more expensive but with longer warranties along with Newegg prices and ratings

• HGST Ultrastar 7K4000. 2M MTBF, unclear TB/year, 600K L/uL, (4/5 $250 Newegg, $240 NCIXUS and $220 Amazon) HUS724040ALA640(0F14688) for native 521 byte sectors SATA PC PartPicker), HUS724040ALS640 for SASWD Red Pro, 1MTBF, 180TB/year, 600K Load/Unload,
• Seagate Constellation ES.3, 1.4M MTBF, 550TB/year,  600K L/uL, $250 (4/5 rating Newegg and $250 at Pcpartspicker for ST4000NM0033)
• Seagate Enterprise Capacity v4. 1.4M MTBF, 550TB/year, 600K L/uL, ($308 at PCPartsPicker and 5TB is only $30 more), $366, ST4000NM0024

As an aside, like all these vendors, HGST has a confusing coding system but to take it apart it works like this:
HUS724040ALE640 = 4TB, SATA 6Gb/s, 64MB buffer

• H = HGST
• U = Ultrastar
• S = Standard
• 72 = 7200rpm
• 40 = Full capacity 4TB
• 40 = This model is 4TB
• A = Generation code
• L = 26.1mm height
• E = Emulated 512 SATA  or A= native 512 or S = native 512 SAS
• 6 = 6GBps interface
• 4 = 64MB cache
• 0 = no encryption, 1= encryption

As a triple aside, the issue of format is decently important. Disks that are natively 4K (called Advanced Format) are 7% or so more efficient and have better error correction. But since most operating systems only know how to deal with 512 byte sectors, the 512 emulation mode is very common. Notably, Mac OS X since Tiger can support 4K native and Synology since 5.1 supports 4K native, but only when they are managed separately from 512e or 512n drives.