Kraken is getting the shout out for being the first exchange to take some serious steps towards proving their bitcoin solvency. Their solution ( https://www.kraken.com/security/audit ) is not perfect but it's better than what any other exchange has done so far. It's going to be just 2 weeks because it's not a full proof of solvency i.e. it still depends on trust to the auditor. I'm happy to promote them because based on my talk with them my subjective opinion is that they know what they are doing.