SAT/ACT
The SAT/ACT is the bread and butter of any contending college application. In many cases, a good high school career can start or end with the score you get on these exams.
Of the two, the SAT is the more popular option, and is continuing to rise in popularity compared to the ACT. Both exams, however, test on comparable material, and many of the skills learned for one may translate easily to the other.
Scholastic Aptitude Test
Scored from 400-1600
Average about 1050 (varies by administration)
Two sections with two modules EACH (adaptive and nonadaptive reading and writing, adaptive and nonadaptive math)
Fully digital (though in-person)
Taken by 1.9 million students annually
American College Testing
Scored from 1-36
Average about 19.5 (varies by administration)
Four sections (reading, writing, math, and science) with an optional writing section
Digital (in-person) or paper versions
Taken by 1.4 million students annually