Verdict

These two are closely matched CMR NAS drives of the same capacity - decide on price and warranty. Check the live $/TB above.

ST18000NM000J WUH721818ALE6L4
Capacity 18 TB 18 TB
Recording tech CMR CMR
RAID / NAS safe Yes Yes
Class Enterprise Enterprise
Spindle speed 7200 RPM 7200 RPM
Cache 256 MB 512 MB
Noise (idle) 29 dB 20 dB
Fill Helium Helium
Interface SATA SATA
Failure rate (AFR) - -
Price / TB $33.61 $28.26

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.