Haven't heard the name kucoin till now, looks pretty now but as binance is having good trading volume lately.
I am still using bittrex and hoping they will not just suspend me like they have done to thousands of bittrex accounts.
Polo is still struggling to resolve all support tickets....
We'll if you want to try it...consider my referral (see my signature)

As I said, they had problems initially but seem to have been resolved. They also offered their coin (5 KCS) to all users as an offering for the make amends for the trouble.
Most my trades at one time was with POLO...now I have nothing there and mostly use Binance, Bittrex and KuCoin now.