Overall poloniex is good exchange as it is considered as one of the best exchanges in the world. And it is right because there are so many reasons such as it provide low trading fees. It provides high security as we need to verify our account by providing national I'd card to them.
I think this exchange has lot of availability of best coins in the world. There platform is too much easy to use and easy to trade . They also provide tutorial for using there exchanges. I think overall it is the best I have used.