Offline. Put the wallet .dat files on a usb stick and keep them safe.
The USB Stick should be clean and free of viruses, or else it will be a mess for the user in case something bad happens (the data got corrupted/lost) to the USB stick. Also, a nice thing to do/consider is to have multiple copies of the wallet files in separate/different USB Sticks that are also free of viruses so that in case one got its data corrupted/lost, you will still have a copy of it.
Hardware wallets are best and modern idea of securing bitcoins. But not viable for everybody when we consider the cost needed for buying it.
A Password protection to encrypt your wallet is more than enough way to secure our bitcoins.