for the safest online wallet is only in blockchain.info but the wallet can only save bitcoin shape only, if you want to save the coin that suport with ERC20 then you can use https://www.myetherwallet.com/ for the real security of all wallets very safe it depends on you just how you keep your secret password or secret key to enter in your wallet, so save the secret key that is given to open your wallet safely and save with encryption code if needed.