The one thing to determine before making a decision is what is actually required or recommended by the colleges you intend to apply to. For example, you need only two unless applying to Georgetown which strongly recommends three. But which two you need depends on colleges and desired major. For example, if you are applying for engineering or science, many of those that recommend two subject tests also tell you that for those majors, they want to see a math and a science… If applying for a business major, some want one of the test s to be a math. As to other majors, a number mention that they would like to see a subject test related to your requested major, e.g., if applying for history, best is for one of them to be history. So make sure you research the universities you are interested in before deciding what to do.