Each class of hard drives is purpose-built for a specific application. Here is a quick table showing major HDD classes in WD and Seagate with their warranties and the purpose they are built for.

Series Purpose-Built for Warranty Description
Seagate Exos Enterprise Data Center 5 Years Limited The highest grade drive can be used anywhere - NAS, surveillance, Data Center. Available in SAS and SATA
Seagate Ironwolf NAS 3 Years Limited The only Drive that offers Data Rescue service for free.
Seagate Ironwolf Pro NAS 5 Years limited Non-stocking item. Generally, it's easier to buy the Seagate Exos Enterprise drive instead
Seagate Skyhawk Surveillance, Video, Smart Video Analytics 3 Years Limited SATA up to 8TB. For use in DVRs and NVRs
Seagate Skyhawk AI Surveillance, Video, Smart Video Analytics 5 Years Limited 8TB+. Higher than Skyhawk
WD Red NAS 3 Years Limited SMR.Meant for usage in NAS storage up to 8 bays
WD Red Plus NAS 3 Years Limited Same as Red, except its CMR
WD Red Pro NAS 3 Years Limited Meant for NAS up to 24 bays. Non-stocking item. Generally, it's easier to buy the WD Ultrastar Enterprise drive instead
WD Purple Surveillance, Video, Smart Video Analytics 3 Years Limited Surveillance drive for use in DVRs/NVRs
WD Ultrastar Enterprise Data Center 5 Years Limited The highest grade drive can be used anywhere - NAS, surveillance, Data Center. Available in SAS and SATA
WD Gold Enterprise Data Center 5 Years Limited Same as Ultrastar. Available only in SATA