Always paper or alternate way of cold storage. i cant really trust with hot storage devices for certain reason. i will just print my keys, laminate them and place them fire secured place. or i would do something similar like craving the key on metal or something like this. paper wallets are easy to deal with. on another hand hot storage like Ledger Nano S can be very expensive and vulnerable at the same time. i can print multiple keys with paper and place it all the secure place for back up. i cant do that with hardware wallets. though paper wallets serves best back up option.