For the California State University system, test scores are required unless you have a grade point average (GPA) above 3.0 and are a resident of California. The CSU uses a calculation called an eligibility index that combines your high school GPA with the score you earn on either the SAT or ACT tests. Even if you have a GPA above 3.0, it is useful to take either an SAT or ACT as the score may indicate if you do not need to take English and math placement tests after you are admitted and before you enroll at the CSU.
While SAT/ACT test scores are not required to establish the admission eligibility of California residents with high school GPA of 3.00 or above (nonresidents 3.61 or above), impacted campuses and impacted first-time freshmen enrollment categories often include test scores among the supplemental criteria required of all applicants to those campuses and enrollment categories.
The University of California system requires the SAT with Essay or the ACT with writing no later than December of your senior year. The UC uses admission test results not only to assess academic preparation and achievement, but to help us determine qualifications beyond what the UC sees in students' grades. The UC will focus on the highest combined or total score from a single test date from either the SAT or ACT.
Four-year colleges accept either the ACT or the SAT in admission selection so it is up to you!
The best way to decide which test is right for you is to take a full length practice test in each. Since the content of the SAT and ACT are similar it is best to figure out how you may deal with the different time-pressure and what questions you find more challenging.
The SAT is a problem solving, critical thinking based test consisting of three 800 point sections. Students are tested on their math, verbal and writing abilities. The SAT tests vocabulary much more than the ACT and is not entirely multiple choice. The maximum score is 2400 with a quarter point deducted for each wrong answer.
The ACT is primarily a content and curriculum-based exam consisting of math, reading, science reasoning and an optional writing section. The ACT math section includes trigonometry; the SAT does not. The maximum score is 36 points, with no penalties for guessing.