Binance, Hitbtc, Bittrex, Pholonex are good exchanges to trade your altcoins with.
Be aware using Poloniex because it has a lot of scam accusation in this forum. I would never trade any big amount there. Although I neber had traded there, some accusations made me think Poloniex as a scam site.
at this time I have never traded with Poloniex, indeed there have been several complaints about this exchanger, even though I have never experienced it directly. but I am more careful in choosing a better exchanger now, binance is the best choice at the moment.