Exchanges and online sites are risky because you don't own your private keys for your Bitcoins. They may be hacked or just shut off - with your money. Best way is keeping them in a wallet where you control your private keys - and for extra security a hardware wallet.
The hardware wallet with full sync is the most secure wallet, this wallet also help to secure bitcoin network. Trezor is good, but actually using online wallet such as blockchain .info which has famous brand name is good. If you still afraid, you can use 2FA to add extra layer of securities in that online wallet.
I don't keep my bitcoins i sell it if i can make some money with it. Because if i keep it i will probably lose a lot of money because i have -10 luck.
So i just buy at low price and sell at high price to make some money.