Some exchanges are safe enough only to have a trade and go out. Since exchanges now are not totally hacker proof it is safe to store money not on exchanges.
If you use the exchange to trade then how it is safe to holding the fund mate. I may agree that you can find the way to do the trade alone but will not be able to hold in any exchange for it mate. If you want to use the good exchange means please use the Binance, Bitrex, Bitfinix and Etherdelta.
For hackers you can see this is the easy way to reach your fund when are looking to hodl.
Please have some private key secured wallet for having your fund be safe.