I suggest you to start your trading on Poloniex and it allows user to trade all the altcoins.Poloniex exchange is one of the exchange that has been running for more years.Some trading sites stopped accepting the new registrations but I think it is not yet in Poloniex so you have to register faster or the chance is their for registration will be closed.
Poloniex also offers low fee when compared to Bittrex exchange.So I hope you got enough information for picking up your exchange.