Well it depends upon on you, the one that you can easily used is the best exchange. The one that you don't experience some problems about trading, depositing, withdrawing, and by means of using it comfortably.
For me I usually used binance because it has an app that has good system ui, easy to use, user friendly, and fast withdrawal process with only 2 confirmation in blockchain network. I also like bittrex and livecoin as I used it also in trading but bittrex has high fees in withdrawing your funds unlike livecoin that has less fees like as binance.

So if your trying to pick your best exchanges, you should first experience them all to have an idea which is good or what is ideal exchange for your future trades.