Bittrex is a good platform to trade your coins on but recently few country's accounts got blocked by them. Those country's users have to upload their identity so that their account can be unlocked. Poloniex is also a good place to trade your coins on.
I think poloniex is not a good place to trade right know. Because poloniex has had some issues. Bittrex is the best exchange in current market. Traders are also like to used in Bittrex. This is the best foreign exchange and it will be directly moves to BTC wallet in Bittrex. Then it will processed in coinbase or local bitcoin. Most traders are having us dollar only. So Bittrex is the more profit to exchange in USD to BTC.