In trying to determine which test to take my first response would be - take both! But, if you really want to focus on only one, keep the following in mind: ACT - less time permitted for each question SAT - section on science no science essay is optional essay is required has trig. questions no trig. questions no guessing penalty guessing penalty The above is a partial list of the differences but the differences don't really help you to determine which test you might be better suited for. Try to think about yourself as an individual. Do you like logic, doing puzzles, brain teaser type of questions or, do puzzles drive you crazy and brain teasers you find annoying? If you like the puzzles and brain teasers, the SAT might be more for you. On the other hand, if you have been able to retain information easily in your high school classes, enjoy reading assignments and discussion and, science is an area you do well in then, the ACT might be for you instead. Again though I would encourage you to take both and see what your level of comfort is for each.You can do practice tests for both SAT and ACT which can help you to decide as well.