Which one is the safest way to store bitcoins? I often hear that becomes thefts. I guess some of them are not heard even.
If you're only looking for the safest way, then cold storage solutions such as paper wallets, hardware wallets etc. are the best. Simply because an online attacker cannot take the coins from you.
But if you're looking for a convenient way, I suggest blockchain.info which is probably the most secure of the online ones.