If you are planning to work in a European or Canadian employer for European or Canadian customers, I think the Master of Science (MSCS) degree may make you more employable ... depending upon your area of concentration. If you are planning to continue your studies for a PhD in Computer Science, I think the MSCS would provide better preparation than the MCS. Only consider a second Master's degree if you plan to earn an MSEE with a computer engineering or digital signal processing emphasis or an MS in Computer Engineering, something very practical.
If you are planning to work for an American employer for American customers, I think the MCS degree with as much business or project management coursework as possible. Make the degree as immediately practical as possible.
Too many advanced degrees, as well as industry certifications, can be detrimental to your professional advancement. If you have to choose between and advanced degree and spending time as part of an open source development effort, choose the open source development effort -- keeping a portfolio of the code you wrote. You can count the time you spend on the open source effort towards your years of experience.