OKEX - the volume of some coins and tokens here is very big. I have opened an account with it but haven’t used yet. For now I’m using these, in order of frequency and value: Bittrex, Binance and Poloniex.

Each has its strengths and issues. The fee charged for withdrawing to my own wallet is an important consideration. Generally Bittrex tends to have the lowest, especially for ERC20 tokens. But not for Bitcoin (at 0.001 BTC) - it’s half that at Poloniex.

Binance withdrawal fees tend to be the highest, especially for ERC20 tokens. However, it has more coins and tokens listed and often tighter spreads between Buy and Sell.