I can only reply based on the exchanges that I have tried. For me BANCOR is the best exchange that I have gotten into so far. It automatically converts your coin and no need to wait for it to be sold. The only thing I don't like about is that the way it accept coins are different unlike other exchanges wherein you just have to get the wallet address to send the coin to. Hitbtc and Yobit are also good since I haven't gotten any issues with it.