Poloniex is one of the big and historical exchanges. they also have many daily users meaning that the volume is large. Another aspect I like is the simple and sober UI of this exchange. It's very useful for beginner to get used with the crypto trading but also for hardcore traders with their advanced charts. I never faced any major issue at that time on poloniex and still I am using it. Among all exchanges I have already experienced, Polo is definitively one of the best. See full review