I will not contradict others when they recommend a hardware wallet, it is one of the safest ways to keep our private keys in the most secure environment. All you have to do is save the backup in at least 2 or three copies in safe places (preferably different locations), and always check that any information on the screen of the device is identical to what we see in the user interface.
Maybe, it is considered one of the safest ways, but a paper wallet could even be safer due to the nature of it. However, what I would say is hardware wallets are particularly good for wallets that need to be accessed frequently, and still have good security. Ideally, the perfect setup in my opinion would be something like a paper wallet, or at the very least a wallet hosted on a offline computer which would act as your stockpile of Bitcoin, that you are holding for long periods of time. Then, a hardware wallet for moving coins about on a frequent basis.
The only improvement over this would be the have multiple wallets without it becoming confusing to store your Bitcoin that you wish to stockpile, so that if one is compromised then the others aren't, and therefore you don't lose your entire Bitcoin net worth.