I think, Blockchain.io will be better crypto to crypto exchange, since their main focus are building crypto exchange that is user friendly and custodial through centralized order book to optimize speed and liquidity, and also combine it with decentralized settlement services that guarantee the anonymous, privacy, and security of transactions, using latest advanced cryptographic technology such as Atomic Swap and Lightning Network. Full centralized exchange is very risky related to Hacking attack, but also Full decentralized exchange brings you to no custodial and slow trading performance. So, it's better to combine both.