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
you think it's so easy to get to such a site)? The more abrupt the exchange the more difficult. if on yobit or cryptopia it is possible to get paid then for larger ones it is more difficult. although cryptopia is not the worst choice. so also hit btc