Hi; The best is "bittrex, poloniex, liqui, hitbtc" but to be accepted on these exchanges, it takes a lot of development, a high quality website, a good explorer ......
But for GCN, since this piece moves step by step; I think yobit or livecoin and especially coinexchange and gatecoin the best exchanges (we will enlarge the community GCN on coinexchange and gatecoin)