Basically, I dont keep much on exchanges / Online wallet for the sake of security and peace of mind. A hardware wallet such as trezor and ledger is always recommended to store bitcoins and is the safest choice.

Though, when I do use an exchange for trading purposes, I make sure I withdraw the funds immediately to my hardware wallet. The only thing which I feel like a problem is that 90% of the altcoins are not supported by these hardware wallets so sometimes I am forced to keep the funds on an exchange.