Nothing is safe in this world, especially in the crypto currencies industry. Just look at this forum and count how many posts about hacking are posted every day. However, a hardware wallet is much safer as a regular MEW.
It's true that nothing is safe but hardware wallets conduct updates so if they find out some faulty on their software, they are updating it immediately so that there will be no backdoors open for their hardware. MEW is good for those who can't avail hardware but coins to be stored there is limited just for ethereum and erc20 tokens. While having a hardware wallet, you have more security and you can hold the supported coins that it has not just those two types.