The safest wallet is a desktop wallet. I recommend that you use Electrum if you want SPV or Armory if you want a full node. Both can be used in the safest manner which is having a dual computer setup, an offline computer and an online one. The offline computer signs the transactions while the online computer is only able to lookup transactions and create the unsigned transaction. Because the online computer doesn't have the private keys, if it gets a virus, the virus can't steal your Bitcoin. The offline computer is unable to connect to the internet so if it somehow gets a virus, then the virus cannot communicate with the attacker to steal your private keys.