While both SAT & ACT tests have quite a lot in common as they both focus on content based testing. However they do portray a difference in testing styles, where in SAT Questions are evidence and context-based in an effort to focus on real-world situations and multi-step problem-solving, ACT questions may be long but are usually less difficult to decipher.
In the Sat exam Math and Evidence-Based Reading & Writing are each scored on a scale of 200-800, and the composite score is the sum of the two section scores and ranges from 400-16000. But in ACT English, Math, Reading, and Science scores range from 1-36 and the Composite score is the average of your scores on the four sections; ranges from 1-36.
In comparison to ACT, SAT consists of the Math section with higher difficulty level while the reading section is more relaxed. In contrast the ACT carries a random difficulty level within its reading and english sections however has a progressive difficulty level in the quantitative section.
Given the above information, SAT seems to be an easier exam for students who are good in math and calculating on the move. However if a student is fast and a good reader, they should opt for the ACT exam.