Both are good cryptoexchanges but binance is already so established since it's already been doing the business for quite some time now. With so many cryptos listed on binance, i believe that binance is more utilized than its newly counterpart in the name of Kucoin.
Of course, Binance is better than Kucoin, at Binance we can see a very high volume of coins than in Kucoin,
and that I think this makes people prefer trading in Binance than in kucoin.
I never had an experience trading in binance but kucoin is a very good market to invest since it does not get any problems in the long run and investors did not lost any of their coins.