Verdict

Both are CMR drives suitable for NAS. The ST12000NM000J has the lower measured failure rate (0.42% vs 2.97% AFR), making it the safer long-term choice.

HUH721212ALE604 ST12000NM000J
Capacity 12 TB 12 TB
Recording tech CMR CMR
RAID / NAS safe Yes Yes
Class Enterprise Enterprise
Spindle speed 7200 RPM 7200 RPM
Cache 256 MB 256 MB
Noise (idle) 20 dB -
Fill Helium Helium
Interface SATA SATA
Failure rate (AFR) 2.97% 0.42%
Price / TB $33.87 -

Highlighted cells mark the stronger spec for a NAS build. Failure rates from Backblaze Drive Stats where available; $/TB shows once live prices are wired.