Because I use both, for me I find it hard to separate two reputable exchanges that have existed for a long time & and because both have their own strengths I want to believe they complement each other and not really rivals which should be a good thing.
But i suppose if this were a popularity contest, i think finance would win this one thanks to the different products that it has on the market that has helped its name get out there.
I don't know if kucoin has something like SAFU, an insurance for their customers. Which binance has.
I am also using kucoin in some of my trades but haven't checked about their insurance offering.
The good thing in both of these exchanges is they have very good liquidity so it is easy to fill your orders.
Though some don't want to fill-up with KYC, the reason why they are choosing kucoin.
However, I believe it is only a matter of time and kucoin will also ask KYC from all their customers.