Leaving all crypto on a trading platform sounds pretty scary. I heard this is too risky, so it might depend on your attitude, the amount and type of assets, a country, a platform, etc. and probably should be considered on a case-by-case basis. But as a rule of thumb, when it comes to all the crypto you have, the safest way to keep it is in a cold storage they say...
I prefer Ledger Nano S.
Of course it's very risky when you put all your assets in one place, especially on an exchange site that is a third party, there are many risks that come like scams, hacking, etc.
Of course you have financial management in this crypto investment right? use it to divide your assets into several places, not just in exchange site, separate them in online wallets or hardware wallets