Lowest Fees / Trusted Exchanges
GDAX - While GDAX only focuses on the big 3 (Bitcoin, Ethereum, Litecoin), the fees are a standard 0.25% taker & 0% maker type structure. The advantage that I give to GDAX is that it is connected to Coinbase which gives you some great ease of use in transfer of funds to an exchange account with no fee at all.
Binance - This is a hot place for trading altcoins and their trading fees are LOW! Just 0.1% fee for trades and it can be even lower if you use their Binance coin that is built into the platform.
CEX.io - The UK based CEX.io makes the list because while most of the exchanges here have a standard fee of 0.25%, they only charges 0.20% per trade! That combined with a solid user interface make it a winner in my book. They DO accept US customers too!
Kucoin - With the recent troubles for some established exchanges, places like Kucoin have stepped up and given the users what they want. I just got started trading on this platform and it is very similar to Binance where fees are just 0.1%!
CoinExchange - This is a new exchange but has gained some popularity recently with the large amount of coins you can trade and the fees only being 0.15% on average.
