You can store it at Bitcoin Wallet, Blockchain for the safest. And I will suggest that create many wallet if you have a large amount of bitcoin for Protection for hackers. If not one wallet is enough. Store your bitcoins at your wallet and don't share it for anyone for you and your money to be safe.
yes not only blockchain, but yobit and xapo are also trusted wallets where you can store your bicoin , but i think the important thing is that you should not keep your bitoin in one place, because if you are keeping them in one place in a big amount then you are increasing the risk of stealing your bitcoins.
i think i will prefer blockchain the most trusted online wallet, i think your money is about 100 % safe here, you just need to prevent your key from the hackers, because they search for such account from where they can easily get bitcoin.