The best way to keep your bitcoins safe, is to use a hardware wallet that have stronger cryptography that web wallets.
If you store your coins in exchanges you are most likely to lose them, because exchanges receive the most cyber attacks.
True, the system of bitcoin itself is secure but the third party that handles bitcoins are quite unreliable specially the exchange platforms. Majority of bitcoins hacked came from these so called exchange sites so you wouldn't want to fully trust does sites.