Binance is step by step becoming the best one from my point of view (lots of altcoins, noob friendly, good spirit, bounties everywhere, community votes)
Recently, there is also COSS (they project to pay the token holders with half of the fees)

Have in mind that these are decentralized exchanges, they are still new technologies, but i prefer that to centralized ones like Bittrex or Poloniex...

If you register on Binance, please use my referal link it would be awesome https://www.binance.com/?ref=10798111