Airgap wallet device would be most the secured way to handle funds. Safest? Nothing is safest, its because it will depend on the user practice of using the wallet, like how you are sending funds from it. There are recommended practice on how to do it, as long as you follow those steps then you are fine. It's the same on using hardware wallets, which will only second from airgap wallet. Safety are all depends on users practice.
Safe or safest, it is individual issue and practice, it not on theory.
In theory, airgap wallets are best and safest but depends on a personal practice with his airgap wallet and that device, it can turn an airgap wallet to a hot wallet. If practice is done like this, from an initial airgap wallet to a hot wallet, it will be surely no longer a safe wallet and can become a worst wallet practically for that person.
If you have bitcoin, stores it in any wallet but at the end your wallet was hacked and you lost all your bitcoin, it's a worst wallet for you.