My favorites exchanges is binance, kucoin, trocaninja and etherdelta (decentralized exchange).
To me I mostly use bittrex , but some time it depend on the currency where you are interested to trade. You need to use the exchange where it is listed. Some time I get some information about a coin and want to do investment there, so for that I have to use the only exchange which is listed there, and cannot use another exchange where the particular coin do not exist.