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No need to look further, we have big exchanges with high liquidity so no need to look for more. I personally use binance, bittrex and hitbtc.
I list some though these are common things that we should look up to.
Privacy
Security
Liquidity
24/7 support
Instant deposit and withdrawal
Yeah binance bittrex hitbtc that's (3) three exchange is the most popular as of now and I included poloniex is also one of the most oldest trusted exchange with low transaction fees with strong private keys for the security of the users i am not promoting poloniex or any exchange but base on my own experience i give my own best for those people want to know is the best all about in trading.