i just traded altcoins on poloniex, there is leverage features at poloniex, and sometime i used cex.io for trading bitcoin to fiat because there are many method to make deposit who be supported by my country and it is safe for me.
I trade mainly in the Poloniex. It is an OK exchange. But it has too many scam coins there. I only trade good coins.
As other traders said that poloniex is good exchange because they removed shit or scam coins there like c-cex .unlike on yobit they not removed many of that kind of altcoins but its good to trade on it if you know what coin to trade on.