It depends on your career goals. The MBA is a general broad degree covering a wide variety of business issues and training students for careers in managing any area of business up to CEO. MBA students study accounting, finance, marketing, statistics, management, economics, strategy, policy, leadership and similar courses. The MBA was developed because people with technical backgrounds getting promoted into management are not always able to manage, and people in management often don't understand the technical fields they manage. That's why MBA programs prefer students with degrees in other than business and with 2-4 years of work experience. Their graduates learn to manage and can speak the language of the people they manage, whether that is engineering, chemistry, medicine, music, or any other field.
The MS is a degree that concentrates study in a specific field, such as finance, accounting, electrical engineering, biology, or chemistry and trains students for careers in high level staff positions often involving research.
Before you consider which MBA program is for you, consult the Official MBA Guide, a comprehensive free public service with more than 2,000 MBA programs listed worldwide. It allows you to search for programs by location (US, Europe, Far East, etc.), by concentration (finance, marketing, aviation management, health management, accounting, etc.), by type of program (full-time, distance learning, part-time, etc), and by listing your own criteria and preferences to get a list of universities that satisfy your needs. You can use the Guide to contact schools of your choice, examine their data, visit their web site, and send them pre applications. You can see lists of top 40 schools ranked by starting salaries of graduates, GMAT scores, and other criteria. It's the best service available at http://officialmbaguide.org.