only a properly created cold storage or a trusted hardware wallet.
you can search for some hardware wallets if you are not tech savvy or don't want to bother learning how tos and if you are willing to pay. things such as Trezor or Ledger nano would work.
or you can learn more about cold storage and do it yourself easily. like creating a paper wallet with tools such as
https://github.com/pointbiz/bitaddress.org or make a Trezor like cold storage on your USB disk yourself
https://en.bitcoin.it/wiki/Cold_storageAlthough it may be open to hacking and other forms of Internet anomalies. I think keeping bitcoins or altcoins in an E-wallet is fairly safe if you would just keep your wallet code to yourself, since it's encrypted, and not hand it out like any piece of random information to anyone. You can also keep a copy of that code in a USB or your own personal computer. Another important thing you should remember is to not be baited by some airdrops sites or the likes that asks for extensive information about your wallet information, that can be an indicator that they may be scammers or hackers.