We know that Bittrex and Poloniex are the most sought after exchangers.
But I want to know which one is best to trade? and I want to know why.
Thanks.

There are many exchanges in currency world or currency trading system. Bianance, Hitbtc, Bittrex, poliniex, cryptopia, Etherdelta, IDEX. Above all exchanges I like Bittrex and poliniex both.