We wrote a neat Spread Indicator that displays the Spreads from 5 of the most popular brokerages, i.e, Poloniex, Binance, Bitfinex, Bittrex and Bitstamp. See the attached screenshot. From what I see, Bitfinex has the lowest spreads and Poloniex floats around the midline.. and the good news is that the spreads at these brokers is much lower than what I expected to see!