The safest wallet for storing ethereum is the one that does'nt store on the internet. One of the best example is trezor, ledger and paper wallet. These wallets are the safest but has also a little bit disadvantage if you loose this device or the paper wallet, all your coins will loose forever. But the safest wallet now that is on the internet is metamask for storing ethereum. You can also import metamask in myetherwallet. Very convinient to use. This is only my opinion regarding the topic.