This is a rather difficult question and I will explain why. Many people know that the last minus 10 percent was caused by the hacking of the Chinese exchange and theft from there a fairly large number of funds and this affected the rate of both Bitcoin and many altcoins and the crypto-currency market fell by 10 percent. That is, to keep money on the stock exchange does not seem to be the best solution, because there are many security issues. On the other hand, wallets are also not so secure, because we've all heard about hacking MEW and today MEW is the best wallet and I'm sure that this wallet is available for every participant of this forum.
The best on reliability of a purse which now you can buy, it is a hardware wallet. For example, I use the hardware wallet TREZOR, but in the use of this wallet there are nuances, as it is designed only for a certain number of coins.
As a result, I think that it is better to store money still on the wallet, but on the other hand more profitable and cheaper coins can be purchased on the exchange, and the reliability they are approximately the same.
In my point of view, everything depends on a portfolio, aims, and tasks. As for me, I have a lot of small coins divided into small parts on 5-7 different exchanges, and some ETH that I hold in 3-4 mew-wallets (in case of a hack). There's no universal recipe. All I can advise is not to hold all your money in 1 place, even if it's a hardware wallet!
