I stored all may bounty tokens in Myetherwallet because thia wallet is the most commonly used by all people in crypto world. But if you are using MEW wallet you need to make sure that no one will know your private keys to avoid getting scammed.
I store most of my tokens on exchangers site and i believe my tokens will safe there. Most of exchangers have good sercue system a cold wallet to avoid hackers.
But if you want to hold tokens for really long time, you need to store on Trezos or somethings like that.