Safest way will be always cold storage, a computer that is offline no internet access via LAN or WiFi (ideally not present at all) Wallet is created in an offline environment. You can buy hardware wallet that is very secure, impossible to lost coins once you get to know how to use it, even your computer is compromised and someone has access in order to create transaction you will need to put the PIN code on your wallet and confirm the transaction. Most popular hardware wallets are Trezor and Ledger Nano S. Next step down is wallet on your PC - for Bitcoins Electrum is a good way to go. For Ethereum ERC20 based Tokens - MyEtherWallet is OK. Remember you can check balance in Ethereum explorer no need to login to MEW every time same with BTC using explorer. I use MyEtherWallet - passwords and private key I keep encrypted on offline PC with VeraCrypt (based on TrueCrypt). Cold storage and hardware wallet will be the most secure way to store Bitcoins and other alts.