Be good exchange for trading maybe yes, but be the best is something that can't be decided by someone. But maybe if want to review and give good opinion, i think it is ok. But for me any exchange is good because we can use all of it.
I won't recommend kucoin as the best exchanger so far because Binance has been there before kucoin if am not mistaking and as well as BITTREX. What we should even look out for in exchangers of now are: maximum security of funds and a 24/7 customer service to attend to the community.
Yes there's already some existing exchanges who more popular than KuCoin, binance already taking the number one spot since more and more traders are trusting this platform even there's already some concerns regarding to that hacked issues but since they've got a good set back plans they able to make things still working in favor of their exchange.