Comparing SAT versus ACT
Score Choice: In ACT, you can chose the scores you want to send to colleges but that is not the case in SAT. The College Board always sends all your SAT scores together and there is no chance to hide the score. For the ACT, specify which scores you want to send to a college and this way you can maintain secrecy about the sections you are weak in:
Freely Do Guesswork: There is no negative marking for wrong answers in ACT. So don't leave any question unanswered. If you are about to run out of time and there are questions you haven't gotten to yet, just guess something or mark the answer based on intuition.
Never leave blank: You'll atleast attain a few points for any correct guesses since there is no negative for wrong answers. Just try the method of elimination and see if A and B cannot be the choice, mark something from the remaining choices and your probability to get a correct guess increases by double.
Focus on Accuracy: Accuracy is still more important than bulk, don't mark something out in everything, our focus is not doing bulk of questions but atleast doing the questions correctly that we know.
No Vocab: In the ACT, the Reading Test is completely passage-based with no sentence completions or other highly vocabulary-dependent questions. That implies you must have a basic vocabulary level with ability to read and interpret the passages. There may be vocabulary-in-context questions about the passages, similar to that in SAT.
More Maths Content: ACT will consist of few higher level concepts like trigonometry which are not asked in SAT and also, all those formulas the SAT gives you at the beginning of the section.
Fewer line References: In SAT exam every reading question gives specific line reference. Most ACT questions do not give you line references and are often very easy to understand. You'll have to spend more time to find out the answer than you would on the SAT.
Science: Inclusion of the science section is the one of the major content differences as science section doesn't need actual science knowledge but a simple ability to interpret scientific data. If you're afraid of interpreting scientific data, better go for SAT.
Essay is Optional: If you are not good in writing ACT is a better choice as ACT essay is not included in the composite score.
Time Issues: Time is a biggest obstacle in ACT. Unlike the SAT, where each subject is divided in three sections, in ACT each subject has just one long section and is definitely more time consuming. The actual time per question you have is alike to (or higher than) SAT. ACT requires more of your attention span and optimism. Also because SAT sections are split up, you can do extremely well in maths and average in other maths questions and that will work well. While in ACT, one hard question destroys your timing mindframe for the whole maths test and so timed practice is must.