Both the SAT and ACT are valued exactly the same in the eyes of college admissions offices. They are also very similar content-wise and so which one you take is purely down to your own personal preference. Here are some differences to consider:
Math Section: this is the largest difference between the two tests. The ACT Math covers more content but goes into less depth. Half of the SAT comprises of Mathematics whereas in the ACT it is only a quarter – if you prefer mathematics you may find the SAT is better suited to you
Reading: The SAT requires much more slower, deeper analysis than the ACT reading which is very fast paced.
Science: the science section of the ACT actually doesn’t require any scientific knowledge as it is primarily data analysis – similar sections appear in both the reading and writing portions of the SAT
Whether the test is computer or paper based depends on where you live.
The best way to decide which paper to take is to take full length and timed practice tests for both and see which is better fit for you.
Also be sure to check the availability in your area.