The SAT scores 400-1600 across two sections; the ACT scores 1-36 as an average of four, including a dedicated Science section. Neither is universally easier — it depends on your strengths.
Students strong in fast data interpretation often score relatively higher on the ACT; those who prefer fewer questions with more time per question often prefer the SAT.
Take a timed practice section of each, convert to percentiles, and commit to whichever gives the higher percentile — colleges accept both equally.