For me, the best decentralized exchange is Poloniex because of their good policy and privacy to each of members. But for now they are requiring valid id for the new comers to ensure to proper use of the said exchanges
I want to upset you, but Poloniex is not a decentralized exchange. Decentralized Exchange is something like etherdelta)
Poloniex is a regular exchange like bittrex binance bitfinex
Poloniex is a bad centralized exchange. If you ask for decentralized ones, you can take a look at waves.
Binance will also make their DEX, you can display this from their roadmap. This will be amazing.