When I was in to bounty campaigns, I was making use of many currency exchanges and not sure all of them are still into business. Right now, I am trusting kucoin only but before start using kucoin I was using yobit, c-cex, tidex.com, bittrex.com, stocks.exchange, hotbit.io, b2bx.exchange, sistemkoin.com, next.exchange, zapple.com, coinexchange.io and a lot more but I could recall right away.

I suggest you to chose 1 or 2 exchange and get KYC clear status with them so that you will not face problems later on. If you have exchange registered in your country then open an account with them also.