I would never use an exchange with optional KYC unless I'd done that KYC because if you use it a lot the chances of your funds being frozen are much, much higher than somewhere you've already cleared yourself with.
how do you know? what are the chances? for a lot of people, not giving up KYC documents is worth the risk. that's how i feel myself. i still use unverified accounts for the majority of my trading.
I like no kyc exchanges, please do not advice me to use any kyc exchange. I prefer exchanges that do not demand for kyc or the ones that makes kyc not mandatory?
i suggest binance or kucoin. as with any centralized exchange, there is a non-zero chance of having KYC sprung on you. complaints about this at binance and kucoin are relatively few and far between.