Hello,
I know you should always have your coins on a hardware wallet.
But for my trading position I don't want to put the coins on a hardware wallet because that would be too cumbersome but I want to distribute the coins on several exchanges.
In your opinion, what are the most secure exchanges in the world, i.e. where can I be most sure that the exchange will not go bankrupt, be hacked, etc.?
Nothing is completely safe, you could put portion of your funds into hardware wallet and rest on exchange for trading. So you don't lose it all.
Regarding secure exchange, I'd stick with binance (cliché, I know). There are also dexes available on popular blockchain platforms where it's not like 'you completely hand over money' which you could use, but they come with their different share of risks.