I'd say the exchanges that currently remained to be unhacked are pretty "safe"; probably Binance and Coinbase. But that doesn't mean I'll recommend leaving funds on these platforms. The developers can make the platform as secure as possible, but never secure enough to the point that it's impossible to hack. Exploits will always be a risk.
https://NotYourKeys.org How do you explain these things to the people whom have entrusted their funds and assets to you for safe keeping hoping that what they gave to you is under safe care only to wake up to a sad news of their assets being stolen by hackers. How do you explain all these.
That's why you don't let other people entrust their funds to you. You have not much to gain but everything to lose.