Time is a major factor to consider in testing.
The ACT is generally regarded as being composed of somewhat easier questions (versus the SAT), but the time allotted to complete each section increases the overall difficulty (equalizing it to the SAT). The ACT allots:
45 minutes for a 75-question English section
60 minutes for a 60-question Mathematics section
35 minutes for a 40-question Reading Comprehension section
35 minutes for a 40-question Science section
Comparatively, the SAT is structured such that the test taker is allowed at least one minute per question, on generally shorter sections (25 or fewer questions).