Every college will take either SAT or ACT and if they prefer one over the other, they will convert the score.
E.g. SAT 1300 = 29 ACT.
Since the formatting of the SAT changed, they are about the same test in every way except the optional essay formatting. Students can download a free test from both of their respective websites and take them first. They may also consider taking both since a college may give more money on one over the other.
Both are 4 long sections now. They both have an optional essay.
The SAT has 3 sections: Reading, Writing/Language and Math. It is offered seven times a year. The score can be between 400-1600. Most colleges will Super Score and take the highest scores from different sections in different tests. Students can take an unlimited amount of times.
The ACT has four sections: English, Math, Reading and Science. It is offered six times a year. The score can be between 1-36. The scores are averaged and students can take up to twelve times.
The essay time was increased to forty minutes and new sub-scores were added.