Speed is not important, durability is. What should I buy?
Whatever's cheapest and/or has the best warranty.
Since speed for write/rewrites isn't a concern, even SMR, Seagate Barracuda, WD Blue, WD Red (not Red Plus or Red Pro), Toshiba P300, DT02 and DT02-V are fine. Read speed on SMR drives are the same as non-SMR drives.
Durability is nonsense since any storage device/media can fail at any time, for any reason, with or without notice.
Longevity and reliability is backups. Which you have planned, but the second should ideally be kept offsite in case of a local catastrophe.