coinexchange.io, cryptopia !
why not  start it with the top exchanges players ?  more volume and liquidity and for sure more active 

top 6 is :

1. Bittrex

2. Binance

3. Bithumb

4. Bitfinex

5. GDAX

6. Poloniex

volume arround  13 000 000 000 usd/24 hour

copied from coinmarketcap.com