If you want to store any altcoins then you can use Metamusk Browser Extension. You can hold more than one HUGE amount of altcoins here. But if you want to hold Bitcoin then Electrum wallet will be best for you. Because it is considered a Bitcoin secure wallet.
You meant Metamask wallet. Second is that someone should not hold huge amount of coins on an online wallet. If the amount of coins is huge, the best is to get a hardware wallet. One of the best hardware wallet that can be gotten is Trezor. Trezor is supporting bitcoin and many altcoins. Although, if it is a bitcoin only wallet, Electrum can be used as a cold storage wallet.