I recently built a list of the best altcoin exchanges
https://www.bestbitcoinexchange.io/ which includes the most trustworthy places to trade bitcoin and cryptocurrency. In my opinion, these are the best platforms for serious altcoin traders:
1. Poloniex - solid community reputation, great volumes, excellent interface, good compliance standards, margin trading on major altcoins, fully refunded users after small theft in 2013.
2. Bittrex - good user trust, located in Vegas USA, nice daily volume, trading interface is good, not as many cryptocurrencies listed though.
3. Yobit - a huge range of coins to trade, good for pump & dumpers, professional trading interface, but too many deadcoins can make things confusing.
4. Bitsquare - decentralized & p2p - I can only repeat how amazing it would be if all exchanges were decentralized.
5. Hitbtc - Copenhagen-based, plenty of users, fees remain low.
6. Changelly - Czech cryptocurrency exchange with serious admins, user following is growing but some way to go still.
7. Kraken - not yet there, but slowly becoming a full-on cryptocurrency exchange. Recent listing of Tether (USDT) make it their 10th alcoin available to trade. Excellent community trust for buying/selling BTC.
8. Shapeshift - different from traditional altcoin exchanges, no account needed to swap coins, based in Switzerland, not a custodial platform so less risk
though I know many of you hate yobit in terms of accepting many coins in their trading platform
From what I have seen this feature has actually contributed to their recent growth. Now that Cryptsy is gone, Yobit are the only proactive exchange accepting all new interesting coins.