Probably IDEX is the most convenient and stable for me.
IDEX the preferred of most in the best decentralized exchange but I've been waiting for the announcement of Binance on how's the progress of their testing with the said decentralization.
EtherDelta.. very rare, just for some ShitCoins to trade with no other exchanges.
I have heard a lot of bad comments about Etherdelta so don't have any glance to use it.