For me, I prefer Binance over Kucoin because Binance has more altcoins than Kucoin. I do not care about their interface, I'm interested in quality and transaction fees. Binance did better than Kucoin at that point. So I would choose Binance.
Why selecting on one of them while we can choose booth platform for our trades and they are not far on rankings and service providing since they are so good on their own rights and better to have two or more exchange choices since we might gonna lift up with this since we can do an arbitrage if price differential occur.
I agree, both the exchange have a good service and have a good volumes inside, so we don't need to select one, if possible use each of those exchange
that have a good and honest feedback, if you will look deeper you will find some advantage dealing with arbitrage trades, so better to have accounts and
be familiar with both platform to take this edge and earned.